ALISMATALES Dumortier Main Tree, Synapomorphies

Alismatineae Engl., Syllabus, ed. 2: 73. Mai 1898; Alismatanae Takht., Sist. Filog. Cvetk. Rast. [Syst. Phylog. Magnolioph.]: 461. 4 Feb 1967; Alismatidae Takht., Sist. Filog. Cvetk. Rast. [Syst. Phylog. Magnolioph.]: 461. 4 Feb 1967

Fossils Pennistemon portugallicus is represented by a flower with spirally arranged stamens and pollen with reticulate exine and acolumellate granular infratectum. These and similar pollen grains (Pennipollis type) from the Late Aptian to the Cenomanian are known from Europe, Africa and North America. Pennicarpus tenuis consists of fossilized unilocular one-seeded fruits from the Early Cretaceous of Portugal, which may emanate from the same plants as Pennistemon. Thalassotaenia debeyi and other Maastrichtian and Danian fossils from western Europe comprise leaves similar to those of extant Cymodoceaceae or Posidonia. Numerous fruits from the Late Paleocene onwards of Asia and Europe resemble Ruppia and Potamogetonaceae and have been described under the name of Limnocarpus.

Habit Bisexual, monoecious, andromonoecious, gynomonoecious, polygamomonoecious, dioecious, or gynodioecious, usually perennial rhizomatous (rarely annual) herbs. Usually aquatic or hygrophilous (sometimes marine).

Vegetative anatomy Mycorrhiza absent. Root stele often triarch to pentarch. Phellogen absent. Secondary lateral growth absent. Vessels often present in roots and sometimes in stem (sometimes entirely absent). Vessel elements with usually scalariform (sometimes simple, rarely reticulate) perforation plates; lateral pits scalariform, simple pits. Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids P2cs or P2cfs type (rarely Ss type?). Nodes multilacunar with several leaf traces. Laticifers sometimes present. Schizogenous ducts and cavities with resins and oils sometimes present. Trichosclereids sometimes present. Silica bodies absent. Calciumoxalate as raphides (H-shaped in cross-section), solitary prismatic crystals, or druses, or absent.

Trichomes Hairs usually absent (sometimes unicellular or multicellular, simple, lepidote, stellate, or prickly).

Leaves Alternate (spiral or distichous), compound (rarely pinnately compound) or simple, entire or lobed, often differentiated into pseudopetiole and pseudolamina, with supervolute, involute or convolute ptyxis (rarely absent). Pseudolamina usually developing from leaf base zone (sometimes from upper part of foliar primordium). Stipules absent or as axillary scales inside leaf sheath (rarely lateral); leaf sheath usually well developed, often with axillary intravaginal (sometimes hair-like) scales/colleters, squamulae intravaginales. Pseudopetiole vascular bundle transection arcuate; inverted bundles frequent. Venation usually pinnate or palmate, pedate, curvipalmate, parallelodromous, acrodromous, campylodromous, sometimes reticulodromous (then usually with tertiary veins). Stomata often absent (sometimes paracytic, tetracytic, anomocytic, or cyclocytic; adjacent cells with or without oblique divisions). Cuticular waxes absent. Mesophyll often with mucilaginous idioblasts containing calciumoxalate raphides, prismatic crystals or druses. Schizogenous laticiferous cavities sometimes present. Tanniniferous cells sometimes abundant. Leaf margin usually entire (sometimes serrate to dentate). Pseudolamina sometimes with apical pore.

Inflorescence Terminal or axillary, simple or branched, panicle, spike or raceme, spike-, raceme- or umbel-like, or fleshy cymose spadix, or flowers solitary. Peduncle sometimes laticiferous. Inflorescence bract sometimes large and showy. Floral bracts and prophylls (bracteoles) often absent (lateral bracteole rarely present).

Flowers Usually actinomorphic (sometimes zygomorphic or asymmetrical). Hypanthium rarely present. Usually hypogyny (sometimes epigyny). Tepals (two or 2+2 or) 3+3 (rarely 4+4 or 6+6), all sepaloid or petaloid, or outer tepals sepaloid with valvate aestivation and inner tepals petaloid, crumpled in bud, free or entirely or partially connate, or absent. Septal nectaries present or absent. Disc absent.

Androecium Stamens one to three, 2+2 or 3+3 (sometimes 18 to c. 100, rarely 4+4, 6+3, 6+4 or 6+6), whorled. Filaments short, free or sometimes connate into synandrium, usually free from tepals (rarely adnate to tepals, epitepalous). Anthers basifixed or subbasifixed, non-versatile, sometimes connate into synandrium, usually tetrasporangiate (sometimes disporangiate or 1–12-sporangiate), usually extrorse (rarely latrorse or introrse), longicidal (dehiscing by longitudinal slits) or poricidal (dehiscing by apical or subapical pores, or short transverse slits); connective often expanded (laminar connective outgrowths sometimes perianth-like). Tapetum amoeboid-periplasmodial, with uninucleate cells. Staminodia usually absent (sometimes extrastaminal or intrastaminal; female flowers sometimes with staminodia).

Pollen grains Microsporogenesis usually successive (sometimes simultaneous). Pollen grains sulcate, meridionosulcate (zonate), disulcate, trichotomosulcate, forate (periporate), di-, tri- or polypantoporate, or inaperturate, usually shed as monads (rarely tetrads), bicellular or tricellular at dispersal. Exine tectate or semitectate, usually with columellate (sometimes granular) infratectum, or intectate, reticulate, microreticulate, foveolate, foraminate, scabrate, spinulate, echinate, verrucate, fossulate, psilate, or smooth (rarely gemmate, areolate, rugulate, or striate), or absent.

Gynoecium Carpels (one to) three or six (to c. 100), in one whorl or seemingly spiral, secondarily free or connate at base, carpel plicate or conduplicate; or pistil composed of (one to) three (to 15) usually congenitally fused (rarely free) carpels; carpel ascidiate to intermediate, with completely non-fused canals, seemingly occluded by secretion. Closure by transverse slit occurring together with longitudinal slit. Ovary usually superior (sometimes inferior), usually unilocular to trilocular (to 47-locular), usually with mucilaginous hair on inner side. Style single, simple, usually very small, or absent, or stylodia terminal, lateral, gynobasic (sometimes connate at base) or absent. Stigma capitate, lobate or peltate, or stigmas usually linear, papillate or non-papillate, Dry or Wet type. Pistillodium usually absent (male flowers sometimes with pistillodia).

Ovules Placentation axile, parietal, basal, apical, laminar, or (sub)marginal. Ovules one to more than 100 per carpel, anatropous, hemianatropous, orthotropous, amphitropous, anacampylotropous, campylotropous or intermediate, ascending, horizontal or pendulous, apotropous, usually bitegmic (rarely unitegmic), usually tenuinucellar (sometimes crassinucellar or pseudocrassinucellar). Micropyle bistomal, endostomal or exostomal. Parietal cell formed from archesporial cell or absent. Nucellar cap often present. Megagametophyte usually monosporous, Polygonum type (rarely 10- to 12-nucleate; rarely disporous, Allium, Veratrum lobelianum, Endymion or Scilla type). Synergids often with a filiform apparatus. Antipodal cells usually persistent, often proliferating (sometimes absent). Endosperm development helobial or nuclear. Endosperm appendage (’endosperm haustorium’, ’basal apparatus’) chalazal. Embryogenesis onagrad, asterad, caryophyllad, or solanad.

Fruit Usually a berry, a drupe, a nut, a nutlike or drupaceous fruit, a loculicidal, septicidal or ventricidal capsule, or an assemblage of achenes or follicles (multifolliculus; rarely an indehiscent or dehiscent syncarp with baccate or nutlike mericarps).

Seeds Aril absent. Operculum sometimes present. Testa thick or thin, multiplicative, often parenchymatous (sometimes absent). Exotesta often fleshy and viscid, often with thick epidermal cell walls. Mesotesta sometimes parenchymatous. Endotesta sometimes absent. Mesotestal and endotestal cells usually thick-walled. Exotegmen often reduced or collapsing. Endotegmen tanniniferous or collapsing. Perisperm rarely developed. Endosperm copious, sparse or absent, starchy (starch grains usually Pteridophyte type, amylophilic) or with aleurone and lipids. Embryo large to small (often macropodous), straight or curved, sometimes with starch, well or poorly differentiated, sometimes with chlorophyll. Cotyledon one, not photosynthesizing. Cotyledon hyperphyll assimilating or modified into haustorium or nutrient-storing organ. Hypocotyl internode usually present (sometimes as swollen nutrient-storing organ). Coleoptile absent. Collar rhizoids or collar roots sometimes present. Radicula absent in some genera. Germination phanerocotylar. Seedling with hypocotyl and root well developed.

DNA Deletion of 3 bp in atpA in many Alismatales (and in Acorus), but not in Tofieldiaceae or Cymodoceaceae; mitochondrial intron processing in most Alismatales according to cis-splicing mechanism

Phytochemistry Flavonols (kaempferol, quercetin), flavones, flavone-C-glycosides, flavone-O-glycosides, flavone aglucones, flavonoid sulfates, protocatechinic aldehyde, cyanidin, tannins, cinnamic acid, caffeic acid derivatives (including caffeic acid sulfate), chlorogenic acid, polyphenolic glycosides with caffeic acid, phenolic sulfates (sulfonated phenolic acids), alkaloids, tyrosine-derived cyanogenic glycosides (e.g. triglochinin), steroidal saponins, chelidonic acid, 5-alkylic- and 5-alkenylic resorcinols homogentisic acid and their glycosides, amines, and bitter substances present. Proanthocyanidins rare or absent. Ellagic acid not found. Sulphated compounds frequent in Juncaginaceae and some allied groups.

Systematics Alismatales are sister-group to all Liliidae except Acorus.

Squamulae intravaginales are a synapomorphy of a main clade in Alismatales (cf. Acoraceae). These structures are intravaginal or axillary non-vascularized scale-, gland- or finger-like trichomes occurring in pairs or multiples in the leaf axils. They are usually multicellular and two-layered and secrete a protective mucilage. Tanniniferous cells are often present at their base, in the middle parts, at the distal end or at the tooth-like border. Alismatales are one of the very few monocot clades in which chlorophyllous embryos have been found. Furthermore, Alismatales comprise most entirely marine angiosperms and the only known marine flowering plants, in which sulphated phenolic compounds are frequent. In some Alismatales intermediates between floral bracts and abaxial tepals seem to be present. It has been suggested that the flowers in at least many taxa are actually pseudanthia.

In most Alismatales, the leaves appear to have developed from the upper part of the leaf primordium (cf. Acorus). However, in many Araceae the leaves probably develop according to the normal monocotyledon principle.

Araceae are usually placed as sister-group to the remaining Alismatales, yet an unresolved basal trichotomy consisting of Araceae, Tofieldiaceae and the remainder has been identified in some analyses, and sometimes Tofieldiaceae are recovered as the sister-group either of all other Alismatales or to Araceae.

Apocarpous gynoecium is a synapomorphy of Alismatales except Araceae, according to Stevens (2001 onwards). Alismatales, except Araceae and Tofieldiaceae, are further characterized by the following potential synapomorphies: aquatic habit; stem with lacunae; absence of druses and raphides; absence of indumentum (trichomes) and bulliform cells; squamulae intravaginales often present; pseudolamina often with an apical pore; pollen grains tricellular at dispersal; absence of endosperm in mature seed; and presence of seedling collar and collar rhizoids.

The clade [Alismataceae+[Butomus+Hydrocharitaceae]] is characterized by, e.g.: bifurcating apical meristems of vegetative axes; inflorescence scapose, cymose and bracteate; outer tepals sepaloid and inner tepals petaloid; both perianth whorls with numerous leaf traces; stamens paired; carpels plicate; seed coat exotestal; and presence of flavone-C-glycosides. Butomus and Hydrocharitaceae have the character of ovary loculi with secretion in common.

The clade [Juncaginaceae+[[Posidonia+[Ruppia+Cymodoceaceae]]+[Maundia+[Zosteraceae+ Potamogetonaceae]]]] is characterized by the following potential synapomorphies (Stevens 2001 onwards): linear ligulate leaves with auriculate base; tepals absent or reduced to a retinaculum (‘abaxial outgrowths’ from the stamens); absence of nectary and filaments; pollen grains inaperturate; carpels with complete postgenital fusion; fruit indehiscent; endosperm development nuclear; presence of sulphated phenolic acids; and absence of flavones and proanthocyanidins.

The clade [[Posidonia+[Ruppia+Cymodoceaceae]]+[Maundia+[Zosteraceae+Potamo-getonaceae]]] has, e.g., the following characteristic features: rhizome with endodermis; epidermis with chlorophyll; one apical orthotropous ovule per carpel; fruit drupaceous; embryo with a massive elongate hypocotyls; and collar or base of hypocotyls much enlarged. [Posidonia+[Ruppia+Cymodoceaceae]] lack vessels, have distichous leaves without stomata, and produce filiform pollen grains. Ruppia and Cymodoceaceae have serrulate leaves and two stamens.

The [Zosteraceae+Potamogetonaceae] clade has the following potential synapomorphies: flowers unisexual; leaf sheath closed; leaves with an apical pore (also present in Scheuchzeria); and staminal pair with a single vascular trace. So far, no obvious morphological synapomorphy uniting Maundia with Zosteraceae and Potamogetonaceae has been found. On the other hand, Maundia is still very poorly investigated.

Petersen & al. (2016) found Acorus as sister to all Alismatales except Tofieldiaceae and Araceae. However, Acorus appeared outside of the Alismatales clade in the analysis by Ross & al. (2016).

Ventenat, Tabl. Règne Vég. 2: 157. 5 Mai 1799 [’Alismoideae’], nom. cons.

Damasoniaceae Nakai, Chosakuronbun Mokuroku [Ord. Fam. Trib. Nov.]: 213. 20 Jul 1943; Elismataceae Nakai, Chosakuronbun Mokuroku [Ord. Fam. Trib. Nov.]: 213. 20 Jul 1943, nom. illeg.; Limnocharitaceae Takht. ex Cronq., Integr. Syst. Class. Fl. Pl.: 1048. 10 Aug 1981

Distribution Allmost cosmopolitan, with their highest diversity in North and South America.

Fossils Cardstonia tolmanii comprises fossilized leaves from the Campanian to the Maastrichtian of Alberta. Moreover, fruits and seeds of Alismataceae are frequent in Cenozoic layers from the Eocene onwards.

Habit Usually bisexual (sometimes unisexual: in Sagittaria monoecious or polygamomonoecious, in Limnophyton polygamomonoecious, in Burnatia dioecious), usually perennial (rarely annual) herbs. Aquatic or helophytic. Tuberous stem, corm or stolons sometimes present.

Vegetative anatomy Roots fibrous, often septate. Turions sometimes formed (e.g. in Sagittaria). Phellogen absent. Secondary lateral growth absent. Rhizome in Limnochariteae and allied genera with endodermis (similar to root endodermis). Vessels in roots only, as a single vascular strand (sometimes absent). Vessel elements usually with simple (sometimes scalariform) perforation plates; lateral pits? Imperforate tracheary xylem elements tracheids. Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Schizogenous ducts with milky latex. Calciumoxalate as druses and single prismatic crystals.

Trichomes Hairs unicellular or multicellular, uniseriate or stellate, or absent.

Leaves Alternate (spiral or distichous), simple, entire, often differentiated into pseudopetiole and pseudolamina, with involute or supervolute ptyxis. Stipules as axillary scales inside leaf sheath (primary leaves in some genera with lateral stipules); leaf sheath well developed; intravaginal scales absent? Venation parallelodromous; mid-vein prominent; usually with transveral veins between primary veins; secondary and tertiary venation reticulate; inverted vascular bundles sometimes present. Stomata usually paracytic, with parallel cell divisions of subsidiary cells (rarely tetracytic). Cuticular wax absent. Mesophyll with prismatic calciumoxalate crystals or druses. Schizogenous secretory cavities with latex. Leaf margin entire (sometimes undulating). Heterophylly frequently occurring. Abaxial surface with an apical subepidermal pore. Extrafloral nectaries present or absent.

Inflorescence Usually terminal or axillary, paniculate, whorled, spike- or umbel-like, with one verticil (flowers sometimes solitary axillary). Sometimes with involucre-like bracts.

Flowers Actinomorphic. Hypogyny. Tepals 3+3, free; outer tepals sepaloid, with valvate aestivation, sometimes persistent; inner tepals petaloid, thin, crumpled in bud (in Burnatia reduced or absent), caducous. Gynoecial-septal nectaries present on lateral walls of carpel bases (in Echinodorus also at tepal bases or stamens; in Sagittaria also on staminodia and filaments of fertile stamens; nectar in Limnocharis and allied genera secreted on entire surface of ovaries). Disc absent.

Androecium Stamens three, six (paired, antesepalous, alternipetalous), 6+3 or numerous (18 to c. 100), whorled (often seemingly spiral). Filaments simple, free from each other and from tepals. Anthers basifixed or subbasifixed, non-versatile, tetrasporangiate, usually extrorse (in Limnochariteae and allied genera usually latrorse), longicidal (dehiscing by longitudinal slits). Tapetum amoeboid-periplasmodial, with uninucleate cells. Outer staminal whorl in, e.g., some species of Hydrocleys and Limnocharis transformed into extrastaminal staminodia.

Pollen grains Microsporogenesis successive. Pollen grains 9–30-pantoporate (rarely di- or triporate or inaperturate), shed as monads, tricellular at dispersal. Exine tectate, with columellate infratectum, foraminate, usually spinulate (in, e.g., Limnocharis and Alisma granulate). Pollen grains often starchy. Excess pollen in one carpel grow out of this carpel through flower base and into another carpel (Endress 2011).

Gynoecium Carpels six, nine (to 20, rarely 20 to c. 100), in a single whorl or seemingly spiral, ab initio antesepalous (sometimes on gynoecial bulges), free (secondary apocarpy) or connate at base; carpel plicate and ascidiate. Ovaries superior, unilocular. Styluli terminal, lateral, gynobasic or absent. Stigmas usually linear (in Limnocharis capitate, in Butomopsis and Hydrocleys hippocrepomorphic), papillate, Dry type. Pistillodia usually absent (male flowers sometimes with pistillodia).

Ovules Placentation in Limnocharis, Butomopsis and Hydrocleys laminar-diffuse (lateral, ovules scattered over carpellary surface), in Alismateae usually basal (in Damasonium marginal). Ovules usually one (sometimes two; in Damasonium two to ten), in Limnocharis, Butomopsis and Hydrocleys numerous per carpel, usually anatropous (rarely campylotropous or amphitropous), ascending, apotropous, bitegmic, tenuinucellar or pseudocrassinucellar. Micropyle usually endostomal. Outer integument two or three cell layers thick. Inner integument approx. two cell layers thick. Parietal tissue often not formed. Nucellar cap formed by periclinal cell divisions of megasporangial epidermis. Megagametophyte usually tetrasporic, quadrinucleate, Allium type (sometimes monosporic, quadrinucleate). Synergids usually with a filiform apparatus. Endosperm development ab initio helobial (Echinodorus, Limnophyton, Sagittaria, Limnocharis, Butomopsis and Hydrocleys) or nuclear (Alisma, Damasonium, Luronium). Endosperm haustoria? Embryogenesis caryophyllad.

Fruit Usually an assemblage of achenes (in Limnocharis, Butomopsis, Hydrocleys and Damasonium polyspermum follicles), often with persistent style and sometimes persistent outer tepals.

Seeds Aril absent. Seeds U-shaped. Seed coat testal(-tegmic). Exotesta with thickened epidermal cell walls. Testal cells in Limnocharis thin-walled, with upright ends (in Butomopsis and Hydrocleys with glandular hairs). Tegmen more or less reduced or with thickened cell walls. Perisperm? starchy. Endosperm absent. Basal suspensor cell enlarged. Embryo hippocrepomorphic, without chlorophyll. Cotyledon one. Cotyledon hyperphyll elongate, assimilating. Hypocotyl internode present (in Baldellia long). Coleoptile absent. Germination phanerocotylar.

Cytology x = 5–13 (x = 11) – Chromosomes 2,4–14,4 μm in length (in Limnocharis, Butomopsis and Hydrocleys 2,6–13,6 μm).

Phytochemistry Flavonols (kaempferol, quercetin), flavone-C-glycosides (Sagittaria), flavone sulphates, cyanidin, tannins (Echinodorus, Luronium, Wiesneria), phenolic sulphates, and alkaloids present. Proanthocyanidins usually absent. Ellagic acid and saponins not found. Rhizome containing starch and sugar.

Use Ornamental plants, aquarium plants, vegetables (corms and roots of Sagittaria, leaves of Limnocharis), forage plants.

Planchon, Bot. Mag. 82: ad t. 4894. 1 Jan 1856 [’Aponogetaceae’], nom. cons.

Distribution Tropical and subtropical regions of the Old World, with their largest diversity in southern Africa and Madagascar.

Fossils Fossil leaves similar to Aponogeton have been found in Late Oligocene layers in Central Asia.

Habit Usually monoecious (rarely dioecious or bisexual?), perennial herbs with corm or rhizome. Aquatic.

Vegetative anatomy Phellogen absent. Apical stem meristem usually bipartite. Secondary lateral growth absent. Vessels usually absent (rarely present in roots, with scalariform perforation plates and ? lateral pits). Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Articulated laticifers containing tannins or oils. Calciumoxalate crystals present in rhomboedrical aggregations.

Leaves Alternate (spiral), simple, often differentiated into pseudopetiole and pseudolamina, entire, with involute or supervolute ptyxis. Stipules absent; leaf sheath well developed, with axillary intravaginal scales, squamulae intravaginales. Venation parallelodromous, with transversal veins connecting primary veins; tertiary veins absent (leaves in Aponogeton madagascariensis reticulate, fenestrate, due to absence of mesophyll between veins). Stomata paracytic. Cuticular wax absent. Mesophyll cells in floating leaves with rhomboedrical accumulations of calciumoxalate crystals. Leaf margin entire. Old pseudolamina with apical pore. Heterophylly often present.

Inflorescence Terminal, with flowers usually spirally arranged in one to 15 spike-like, simple or branched, inflorescences above water level (in Aponogeton ranunculiflorus reduced into few-flowered pseudanthia); each inflorescence as young surrounded by a usually caducous spathe-like bract. Peduncle (scape) with articulated laticifers. Floral bracts absent.

Flowers More or less zygomorphic, small. Hypogyny. Tepals usually two (abaxial lateral, corresponding to inner? tepals; rarely one tepal [one tepal possibly adnate to bract]; in Aponogeton hexatepalus six tepals), petaloid, usually persistent (rarely caducous), free (absent in female flowers of dioecious species). Gynoecial-septal nectaries usually present on lateral walls of carpel bases. Disc absent.

Androecium Stamens usually 3+3 (in Aponogeton distachyos eight to 16 in several whorls, sometimes paired). Filaments free from each other and from tepals. Anthers basifixed, non-versatile, tetrasporangiate, usually extrorse (sometimes introrse), longicidal (dehiscing by longitudinal slits). Tapetum amoeboid-periplasmodial, with ab initio uninucleate cells. Female flowers in monoecious species with staminodia.

Pollen grains Microsporogenesis successive or simultaneous. Pollen grains monosulcate, shed as monads, usually tricellular (sometimes bicellular) at dispersal. Exine semitectate, with columellate infratectum, perreticulate, beset with supratectal spinules.

Gynoecium Carpels (two or) three (to nine), alternitepalous, free or connate at base; odd carpel anterior (carpella anterioris). Ovary superior, unilocular (apocarpy). Stylulus short. Stigma adaxially decurrent, papillate, Dry type. Male flowers with pistillodia.

Ovules Placentation basal or marginal. Ovules (one or) two to twelve per carpel, anatropous to hemianatropous, ascending, usually bitegmic (in Aponogeton distachyos unitegmic), crassinucellar. Micropyle ?-stomal. Outer integument usually three cell layers thick. Inner integument two cell layers thick. Parietal cell formed from archesporial cell. Nucellar cap formed by periclinal divisions of megasporangial epidermal cells. Megagametophyte monosporous, Polygonum type. Antipodal cells not proliferating. Endosperm development helobial. Endosperm haustoria? Embryogenesis caryophyllad (sometimes Sagittaria type).

Fruit A multifolliculus with almost free (basally connate) individual follicles.

Seeds Aril absent. Seed coat testal, mucilaginous. Exotesta thick or thin. Mesotesta often parenchymatous. Endotesta present or absent. Exotegmen collapsing. Endotegmen tanniniferous, or thin and undifferentiated. Perisperm not developed. Starch present. Endosperm absent. Suspensor absent. Embryo straight, with or without chlorophyll. Cotyledon one, large, bifacial. Cotyledon hyperphyll elongate, assimilating. Hypocotyl internode short. Coleoptile absent. Germination phanerocotylar.

Cytology n = 8, 12, 16, 20, 28 – Polyploidy and aneuploidy frequently occurring. Agamospermy occurring. Chromosomes 0,7–2,3 μm long.

Phytochemistry Flavonols (kaempferol, quercetin), cyanidin, tannins (in isolated leaf cells), polyphenolic glycosides with caffeic acid, proanthocyanidins, and chlorogenic acid present. Flavone-C-glycosides, ellagic acid, alkaloids, saponins, cyanogenic compounds, and cell wall bound ferulate not found.

Arales Juss. ex Bercht. et J. Presl, Přir. Rostlin: 263. Jan-Apr 1820 [‘Aroideae’]; Lemnaceae Gray, Nat. Arr. Brit. Pl. 2: 729. 10 Jan 1822 [‘Lemnadeae’], nom. cons.; Pistiaceae Rich. ex C. Agardh, Aphor. Bot. (9): 130. 19 Jun 1822; Lemnales Link, Handbuch 1: 289. 4-11 Jul 1829 [‘Lemnaceae’]; Aropsida Bartl., Ord. Nat. Pl.: 25, 65. Sep 1830 [’Aroideae’]; Callaceae Reichb. ex Bartl., Ord. Nat. Plant.: 25, 66. Sep 1830; Orontiaceae Bartl., Ord. Nat. Plant.: 24, 68. Sep 1830; Pistiales Rich. in C. F. P. von Martius, Consp. Regn. Veg.: 5. Sep-Oct 1835 [’Pistiaceae’]; Arisaraceae Raf., Fl. Tellur. 4: 16. med 1838 [’Arisaria’]; Pothaceae Raf., Fl. Tellur. 4: 16. med 1838 [‘Pothidia’]; Orontiales J. Presl in Nowočeská Bibl. [Wšobecný Rostl.] 7: 1653 ['1553']. 1846 [‘Orontiaceae’]; Cryptocorynaceae J. Agardh, Theoria Syst. Plant.: 32. Apr-Sep 1858 [‘Cryptocoryneae’]; Caladiaceae Salisb., Gen. Plant.: 5. 15-31 Mai 1866 [‘Caladeae’]; Dracontiaceae Salisb., Gen. Plant.: 7. 15-31 Mai 1866 [‘Draconteae’]; Colocasiaceae Vines, Stud. Text-book Bot. 2: 541. Mar 1895 [’Colocasioideae’]; Lasiaceae Vines, Stud. Text-book Bot. 2: 540. Mar 1895 [‘Lasioideae’]; Monsteraceae Vines, Stud. Text-book Bot. 2: 540. Mar 1895 [‘Monsteroides’]; Philodendraceae Vines, Stud. Text-book Bot. 2: 540. Mar 1895 [‘Philodendroideae’]; Wolffiaceae (Gray) Bubani, Fl. Pyren. 4: 22. 15-28 Feb 1902; Aranae Thorne ex Reveal in Novon 2: 235. 13 Oct 1992; Aridae Takht., Divers. Classif. Fl. Pl.: 579. 24 Apr 1997

Distribution Mainly tropical but also subtropical regions, and approx. ten genera in temperate regions in the Northern Hemisphere.

Fossils The fossil record of Cretaceous and Cenozoic Araceae is very rich, with a peak during the Paleocene and Eocene (e.g. with the Proxapertites pollen type). Fossils of Orontium have been found in Late Cretaceous and Eocene layers in North America. Fossil stems, leaves, stamens and pollen of Limnobiophyllum have been found in Late Cretaceous to Miocene layers of Europe, Israel, North America and East Asia. Limnobiophyllum had stolons and rosettes of floating leaves or foliaceous branches. This genus has often been interpreted as intermediary between Lemnoideae and other Araceae and is placed in cladistic analyses as sister to Lemnoideae. Fossil pollen grains of Pothooideae-Monstereae are known from the Late Barremian to the Early Aptian of Portugal. These include the Early Cretaceous Mayoa portugallica, if correctly interpreted as a fossil pollen, inaperturate, with striate exine and granular infratectum, similar to Holochlamys in Monsteroideae. Pennipollis may possibly belong here. The Proxapertites pollen grains have a tectate exine, an acolumellate infratectum and an aperture encircling the equator. The infructescence Albertarum pueri from the Campanian of Alberta has been assigned to Orontioideae, and leaves resembling Orontioideae were described from the Early Campanian to Maastrichtian of Europe and North America. Leaves of Cobbania have been found in the Campanian to the Maastrichtian of Asia and North America. Fossil flowers, fruits and seeds occur in Cretaceous and Cenozoic layers of North America and Europe, and Neogene seeds of Araceae (e.g. Pistia) are frequent in European and Siberian lignites. Lasioideaecidites, from the latest Campanian to the earliest Maastrichtian Vilui Basin sediments in Siberia, was assigned to Lasioideae.

Habit Bisexual, monoecious (often with female flowers in lower part of inflorescence and male flowers in middle and upper parts), andromonoecious, gynomonoecious, polygamomonoecious, dioecious, or gynodioecious, usually perennial (rarely annual) herbs (some are giant herbs, whereas others are extremely small [e.g. Wolffia]), often epiphytic or climbing with stem or roots (rarely suffrutices). In the aquatic Lemnoideae, leaves are absent and the stem is reduced to a usually flat thalloid floating structure with or without roots on the lower side. Some genera have a starchy stem tuber (e.g. in Lasioideae and Aroideae). Many representatives are aquatic (e.g. Pistia) or hygrophilous. Turions are formed in, e.g., Spirodela, Wolffia and some species of Lemna.

Vegetative anatomy Roots with mycorrhiza. Water-absorbing velamen, formed from epidermis, present in some representatives (e.g. Anthurium). Root hypodermis dimorphic. Phellogen absent. Secondary lateral growth absent? Vessels present in roots in many species (in some species also in stems). Vessel elements with scalariform perforation plates; lateral pits? Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids usually P2c, P2cs or P2cfs type (in Pistia Ss type). Nodes multilacunar with several leaf traces. Laticifers (simple or branched, sometimes anastomosing) usually present; latex white or colour-less, often tanniniferous. Schizogenous canals and cavities with resins and oils present in some genera. Trichosclereids abundant in Spathiphylleae and Monstereae. Calciumoxalate as ‘twinned’ raphides (H-shaped in cross-section), druses, prismatic crystals, etc. Silica bodies absent.

Trichomes Hairs usually absent (rarely unicellular or multicellular, lepidote, or as prickles; in Pistia ‘jointed’ uniseriate hairs).

Leaves Alternate (spiral), compound (rarely pinnately compound) or simple, entire or lobed (sometimes fenestrate or perforate; rarely peltate), usually differentiated into pseudopetiole and pseudolamina, or absent (in Lemnoideae), with supervolute ptyxis. Stipules absent; leaf sheath usually well developed (some genera with axillary intravaginal hair-like scales/colleters, squamulae intravaginales). Pseudopetiole often with distal pulvinus, geniculum. Vascular bundles of pseudopetiole scattered. Venation usually pinnate or palmate (sometimes pedate, arcuate from leaf base, curvipalmate, parallelodromous, etc.; only in Gymnostachys distinctly parallel), acrodromous, campylodromous etc.; mid-vein compound; fine venation reticulate to parallel-pinnate (parallel to primary lateral veins). Stomata usually paracytic (sometimes anomocytic, cyclocytic, or tetracytic); adjacent cells usually dividing. Cuticular wax crystalloids as non-orientated platelets, threads or tubuli, or absent. Mesophyll often with mucilage cells containing calciumoxalate raphides. Leaf margin usually entire. Extrafloral nectaries present in some species.

Inflorescence Usually a terminal, thick fleshy cymose spadix (in Lemnoideae reduced to one or two flowers) usually with spiral (rarely whorled) flowers subtended by a usually showy bract, spathe, often with odorous appendage (in Gymnostachys, Orontium and Lemnoideae very small or strongly reduced). Floral prophylls (bracteoles) and bracts absent.

Flowers Actinomorphic to asymmetrical, small (in Lemnoideae extremely small and strongly reduced). Hypogyny. Tepals 2+2 or 3+3 (when dimerous then outer tepals lateral; when trimerous then median tepal in outer whorl adaxial; rarely 4+4 or 6+6), sepaloid, scale-like, free or entirely or partially connate, or absent. Septal nectaries absent (perigonal nectaries present in Anthurium; staminodial nectaries in Aglaonema). Disc absent.

Androecium Stamens one, 2+2 or 3+3 (rarely 4+4 or 6+6), antetepalous. Filaments short, free or connate into a synandrium, free from tepals. Anthers usually basifixed (sometimes ventrifixed), non-versatile, sometimes connate into a synandrium, usually tetrasporangiate (sometimes disporangiate), usually extrorse (rarely latrorse or introrse), longicidal (dehiscing by longitudinal slits) or poricidal (dehiscing by apical or subapical pores, or short transversal slits); connective often expanded. Tapetum amoeboid-periplasmodial, with usually uninucleate (some species with binucleate) cells. Female flowers sometimes with staminodia.

Pollen grains Microsporogenesis usually successive (rarely simultaneous). Pollen grains sulcate, meridionosulcate (zonate), disulcate (diaperturate), forate (periporate), or inaperturate (omniaperturate), usually shed as monads (rarely tetrads), bicellular or tricellular at dispersal. Exine tectate or semitectate, with columellate or granular infratectum, or intectate, pertectate, perforate, reticulate or foveolate, smooth, psilate, scabrate, spinulate, or fossulate (rarely gemmate, verrucate, areolate, regulate, or striate); endexine spongy. Pollen grains usually starchy.

Gynoecium Pistil composed of (one to) three (to 15) usually congenitally fused (rarely free) carpels; carpel ascidiate to intermediate, eusyncarpous, seemingly occluded by secretion. Ovary superior, usually unilocular to trilocular (in Spathicarpeae unilocular to octolocular; in Philodendron bilocular to 47-locular), usually with a mucilaginous hair on inner side. Style single, usually very small, or absent. Stigma capitate or lobate, non-papillate, Dry or Wet type. Male flowers sometimes with pistillodium.

Ovules Placentation axile to parietal, basal to apical. Ovules one or few to numerous per carpel, anatropous, hemianatropous, orthotropous, amphitropous, anacampylotropous or intermediate, pendulous, horizontal or ascending, usually bitegmic (in Gymnostachys unitegmic), usually tenuinucellar or pseudocrassinucellar (in, e.g., Calla and Symplocarpus crassinucellar). Micropyle bistomal or exostomal. Outer integument (two to) eight to 26 cell layers thick (at base). Inner integument two to ten cell layers thick. Parietal cell often formed from archesporial cell. Nucellar cap, usually two or three cell layers thick, formed by periclinal cell divisions of megasporangial epidermis. Megagametophyte usually monosporous, Polygonum type (in Nephthytis 10- to 12-nucleate; in Lemna, Wolffia and Wolffiella disporous, Allium or Scilla type). Antipodal cells sometimes proliferating. Hypostase present or absent. Endosperm development usually ab initio helobial or nuclear; first cell division usually very asymmetrical; subsequent initial divisions often entirely in micropylar chamber. Endosperm appendage (’endosperm haustorium’, ’basal apparatus’) chalazal. Embryogenesis onagrad, asterad, caryophyllad, or solanad.

Fruit Usually a juicy berry (sometimes dry or leathery; in Lagenandra dehiscing at base; in some genera fused into an indehiscent or dehiscent syncarp), often with mucilaginous envelope and sometimes partially mucilaginous pericarp; in Lemnoideae a nutlike fruit.

Seeds Aril absent. Testa thick or thin, multiplicative, often parenchymatous (absent in Gymnostachys, Nephthytis and Orontium). Operculum present. Exotesta often fleshy and viscid. Mesotestal and endotestal cells usually thick-walled. Tegmen unspecialized, often collapsing. Perisperm rarely present (in, e.g., Pistia). Endosperm copious, sparse or absent, starchy or with aleurone and lipids. Embryo large to small (often macropodous), straight or curved, with or without starch, usually little differentiated, usually with chlorophyll. Cotyledon one, not photosynthesizing. Cotyledon hyperphyll assimilating or transformed into haustorium or nutrient-storing organ. Hypocotyl internode usually present (sometimes as a swollen nutrient-storing organ). Coleoptile absent. Collar rhizoids or collar roots sometimes present. Radicula absent in some genera. Germination phanerocotylar.

Phytochemistry Flavonols (kaempferol, quercetin), O-flavones, flavone-C-glycosides, cyanidin, ethereal oils (in, e.g., Homalomena), cinnamic acid, alkaloids (including benzylisoquinoline alkaloids), cyanogenic glycosides (triglochinin etc.), steroidal saponins, tyrosine-dervided cyanogenic substances, amines, and bitter substances present as well as several irritating or allergenic substances (e.g. protocatechinic aldehyde, homogentisic acid and their glycosides, and 5-alkylic- and 5-alkenylic resorcinols). Ellagic acid and chelidonic acid not found.

Use Ornamental plants, aquarium plants (Cryptocoryne, Pistia etc.), starch sources and vegetables (Colocasia esculenta, Xanthosoma sagittifolium, Amorphophallus paeoniifolius), fruits (Monstera deliciosa), gels in food-stuffs (A. konjac), medicinal plants, arrow poisons, fibres for basketry, animal forage (Lemnoideae).

Systematics Araceae are sister-group to the remaining Alismatales. The clade [Gymnostachys+Orontioideae] is sister to all other Araceae and characterized by, e.g., continuous tectum, orthotropous ovule, an inner integument three or four cell layers thick and multiplicative, and a seedling possessing cataphylls.

[Gymnostachys+Orontioideae]

Gymnostachydoideae Bogner et Nicolson in Willdenowia 21: 37. 11 Dec 1991

1/1. Gymnostachys (1; G. anceps; eastern Queensland, eastern New South Wales). – Vascular bundles with fibre envelopes and girders. Leaves distichous, linear, without pseudopetiole. Venation parallelodromous. Stomata parallel to foliar axis. Leaf margin finely serrate. Inflorescence complex, branched. Spatha absent. Flowers dimerous. Tepals four. Stamens four. Anther thecae running out in a tip above the slit. Pistil composed of a single ascidiate carpel. Ovary unilocular, with non-secreting? locule. Stigma Dry type. Placentation apical. Ovule one per carpel, orthotropous, unitegmic. Micropyle absent. Testa absent. Endosperm copious, starchy, with chlorophyll. Embryo with chlorophyll. Collar rhizoids absent. n = 12. – Gymnostachys is sister-group to the remaining Araceae, according to some molecular analyses. On the other hand, Cabrera & al. (2008) identified Gymnostachys as sister to Orontioideae.

Orontioideae R. Br. ex Müll. Berol. in Ann. Bot. Syst. 5: 898. 1860 [‘Orontiaceae’]

3/8. Orontium (1; O. aquaticum; southeastern Canada, eastern United States), Lysichiton (2; L. camtschatcensis: Kamchatka, Sakhalin, the Kuriles; L. americanus: western North America), Symplocarpus (5; S. egorovii, S. nabekuraensis, S. nipponicus, S. renifolius: northeastern Asia; S. foetidus: southeastern Canada, northeastern United States). – Temperate East Asia, western and eastern North America. Collenchyma sometimes arranged in cortical bands. Vascular bundles often with fibre strands. Simple laticifers present in Orontium. Sieve tube plastids without starch. Leaves spiral, elliptic. Spatha absent in Orontium. Tepals usually 2+2 (in Orontium usually 3+3). Usually epigyny (in Orontium hypogyny). Ovary unilocular or bilocular. Placentation basal or subbasal. Ovule one or two per carpel, usually orthotropous (in Orontium hemianatropous), crassinucellar. Outer integument 22 or more cell layers thick (integument in Symplocarpus lobate). Inner integument five to ten cell layers thick. Parietal tissue usually present. Endosperm absent or rudimentary. n = 13–15. Flavonols present. Flavone glycosides absent. – Orontium is sister to [Lysichiton+Symplocarpus].

[Lemnoideae+[[Pothoideae+Monsteroideae]+[Lasioideae+[Zamioculcadoideae s.lat.+Aroideae]]]]

Megasporangial tissue disappearing during maturation of the ovule. Endothelium present. (Steven 2001 onward)

Lemnoideae Bab., Man. Brit. Bot.: 320. Mai-Jul 1843 [‘Lemneae’]

5/37. Spirodela (3; S. oligorrhiza, S. polyrrhiza, S. sichuanensis; cosmopolitan), Landoltia (1; L. punctata; southern Asia, Australia), Lemna (12; cosmopolitan), Wolffia (11; nearly cosmopolitan; paraphyletic; incl. Wolffiella?), Wolffiella (10; tropical and southern Africa, southern Asia, southeastern United States to tropical South America). – Mainly temperate and subtropical regions on the Northern Hemisphere, the Andes, Argentina, eastern and southern Africa, Madagascar, South Asia, Australia, Tasmania, New Zealand. Usually monoecious (rarely dioecious). Annual herbs. Floating, aquatic herbs with usually thalloid stems. Roots single, several or absent. Collenchyma and bundle fibres absent. Vessels absent. Venation only as primary veins. Mucilage cells present. Leaves absent. Prophyll present or absent. Spathe extremely reduced, present at side of leaf sheath, or absent. Spadix extremely reduced. Tepals absent. Stamen single, disporangiate (Wolffia and Wolffiella) or tetrasporangiate. Anther dehiscing by transversal or longitudinal slits or pores (sometimes apically). Pollen grains tricellular at dispersal. Exine ulcerate, spinulate. Pistil composed of a single carpel. Stigma infundibuliform. Placentation basal. Ovules one to seven per carpel, orthotropous, anatropous or hemianatropous, ascending, bitegmic, crassinucellar. Micropyle bistomal or endostomal. Inner integument two or three cell layers thick. Parietal tissue one (or two) cell layer thick. Nucellar cap sometimes two cell layers thick. Megagametophyte Polygonum or Allium type. Endosperm development probably cellular. Embryogenesis onagrad or irregular. Fruit an achene. Seed operculate. Endosperm starchy. Embryo undifferentiated. Hypocotyl and radicula absent. Cotyledon sheath wide, photosynthesizing. x = 10. Polyploidy and dysploidy frequently occurring. Flavonols, proanthocyanidins, alkaloids, and cyanogenic substances absent. – Lemnoideae are sister-group to the remaining Araceae (except Gymnostachys and Orontioideae). The thallus is usually interpreted as a combination of a reduced stem and a reduced leaf. The reproductive organ is interpreted as a small bisexual flower or a much reduced inflorescence with a single female flower and one or two male flowers. Spirodela is sister to the clade [Lemna+[Landoltia+[Wolffia+Wolffiella]]]. Wolffia and Wolffiella lack roots and veins on the thallus.

[[Pothoideae+Monsteroideae]+[Lasioideae+[Zamioculcadoideae s.lat.+Aroideae]]]

Araceae sensu stricto

108/3.395–3.430. According to Stevens (2001 onwards) characterized by, e.g., shoot consisting of a reiterated sympodial unit (continuation shoot); branching from the axil of a penultimate foliar organ outside the spathe; pseudopetiole distinctly differentiated from the sheathing base; spathe large and often showy; presence of peduncle; and non-multiplicative inner integument. The collenchyma is of the Type B. Seedling cataphylls may be present or absent. – The Bisexual Climbers clade is sister-group to the remainder.

The Bisexual Climbers clade (sensu Cabrera & al. 2008)

16/>1.420. Stems usually hemiepiphytic, aerial, climbing (plants sometimes terrestrial, rheophytic or helophytic). Vascular bundles often surrounded by fibres. Styloids present. H- or T-shaped trichosclereids usually present. Leaves spiral or distichous. Pseudopetiole distally geniculate. Embryo often surrounded by crystals. Separate cortical vascular bundles may occur, as well as vessels in the stem (Steven 2001 onwards). – Pothoideae are sister to Monsteroideae.

[Pothoideae+Monsteroideae]

Pothoideae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 140. 1876

4/>1.060. Anthuriumclade Anthurium (>1.000; Mexico, Central America, the West Indies, tropical South America). – Potheae Bartl., Ord. Nat. Plant.: 67. Sep 1830 [‘Pothoina’]. Pothos (c 55; Madagascar, tropical Asia to eastern Queensland, northeastern New South Wales and Melanesia), Pedicellarum (1; P. paiei; Borneo), Pothoidium (1; P. lobbianum; the Philippines, Sulawesi, the Moluccas, Orchid Island in Taiwan). – Tropical America, Madagascar, tropical Asia, northeastern Australia, Melanesia. Spadix not enclosed by the spatha. Flowers dimerous or trimerous. Anther thecae often forming a tip above anther slit. Pollen grains in Anthurium porate. Placentation basal-parietal. Ovules one or two per carpel, anatropous?, apotropous. Outer integument six to eight cell layers thick, multiplicative. Inner integument at least sometimes five to seven cell layers thick. Spatha persistent in fruit. Endosperm sparse, starchy, or absent (in Anthurium copious). Embryo sometimes with chlorophyll. n = (10) 12 (14) (15). Seedling internode sometimes long. Unifacial part of cotyledon sometimes very short. Cataphyll absent in Anthurium. – Anthurium is sister to the remaining Pothoideae, Potheae, which are characterized by shoot monopodial, endosperm sparse or absent, and x = 12.

Monsteroideae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 142. 1876

12/c 360. Heteropsideae Engl., Nat. Pflanzenr. 21: 20. 13 Jun 1905. Stenospermation (c 50; southern Mexico, Central America, tropical South America), Heteropsis (17; tropical South America), Rhodospatha (c 30; Costa Rica, Panamá, tropical South America), Alloschemone (2; A. inopinata, A. occidentalis; Brazil, Bolivia). – Spathiphylleae Engl. in Engler et Prantl, Nat. Pflanzenfam. II, 3: 112, 121. Aug 1884. Spathiphyllum (c 40; Central Malesia to Solomon Islands, Florida, southern Mexico, Central America, tropical South America), Holochlamys (1; H. beccarii; New Guinea, New Britain). – Rhaphidophoreae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 143. 1876 [‘Raphidophoreae’]. ‘Rhaphidophora’ (c 100; tropical Africa, Madagascar, tropical Asia to islands in the Pacific; paraphyletic), Anadendrum (12; southern China, Southeast Asia, Malesia to Sulawesi and the Philippines), Scindapsus (c 35; tropical Asia from India to Hainan and Solomon Islands), Monstera (c 50; southern Mexico, Central America, the West Indies, tropical South America), Epipremnum (15–17; the Himalayas, southern China, Southeast Asia, Malesia to tropical Australia and islands in western Pacific), Amydrium (5; A. hainanense, A. humile, A. medium, A. sinense, A. zippelianum; southern China, Southeast Asia, Malesia to New Guinea). – Pantropical (few species in Africa). Separate stem cortical vascular tissue sometimes present. Vessels sometimes present in stem. Laticifers sometimes present. Spatha early caducous. Flowers usually dimerous (in Spathiphylleae trimerous). Tepals often absent. Pollen grains inaperturate, expanded-monosulcate or zonate. Style often with abundant trichosclereids. Placentation often basal. Ovules one to four (to numerous) per carpel, sometimes hemianatropous. Seed often surrounded by mucilage. Endosperm usually absent (present in Spathiphylleae). Embryo often surrounded by crystals. n = 12, 14, 15, 21. Polyploidy frequently occurring. –Heteropsideae are sister-group to the remaining Monsteroideae and have x = 14. Spathiphylleae are characterized by smaller trichosclereids in bundles, and pollen grains polyplicate-multiaperturate.

[Lasioideae+[Zamioculcadoideae s.lat.+Aroideae]]

The Podolasia clade

92/1.975–2.010. Leaves usually spirally arranged. – Lasioideae are sister to the remaining Podolasia clade.

Lasioideae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 144. 1876

10/49. Dracontium (24; Central America, the West Indies, tropical South America), Dracontioides (2; D. desciscens, D. salvianii; eastern Brazil), Anaphyllopsis (3; A. americanum, A. cururuana, A. pinnata; tropical South America), Pycnospatha (2; P. arietina, P. palmata; Southeast Asia), Anaphyllum (2; A. beddomei, A. wightii; Laccadive Islands), Cyrtosperma (12; New Guinea to islands in the Pacific), Lasiomorpha (1; L. senegalensis; tropical West and Central Africa), Podolasia (1; P. stipitata; West Malesia), Lasia (2; L. concinna, L. spinosa; India, Tibet, China, Taiwan, Southeast Asia, Malesia to New Guinea), Urospatha (11; Central America, tropical South America). – Tropical West and Central Africa, tropical Asia, Pacific islands, tropical America. Terrestrial or rooted aquatic (helophytic) plants with tuber or rhizome. Vascular bundles surrounded by fibres. Sieve tube plastids with sparse starch. Laticifers present. Pseudopetiole, abaxial surface of primary leaf veins, and peduncle very often prickly and warty. Pseudopetiole geniculate distally, with Type 4 ground tissue. Type 4 foliar spongy aerenchyma. Order of anthesis basipetal. Anther with oblique pore-like slits. Pollen grain without starch; sulcus unique among angiosperms, with ectexine lamella and thick two-layered endexine: outer layer flaky or lamellate and inner layer spongy. Pistil composed of one to three (to 16) connate carpels. Placentation of various types. Ovules one or two (to numerous) per locule, anacampylotropous, apotropous. Mesotestal and endotestal cell walls lignified. Endosperm thin or absent. Embryo curved, with chlorophyll. x = 13. – The phylogeny of Lasioideae is largely unresolved.

[Zamioculcadoideae s.lat.+Aroideae]

The Unisexual Flowers clade (sensu Cabrera & al. 2008)

82/1.925–1.960. Flowers usually unisexual (in Calla bisexual). Spatha differentiated into ‘tube’ and ‘lamina’. Spadix differentiated into zones with female flowers and male flowers, respectively. Pollen grains usually inaperturate (in Zamioculcas and Gonatopus aperturate). – This clade has weak support in molecular analyses, although the Stylochaeton clade [Stylochaeton+Zamioculcadoideae] may be sister to Aroideae.

The Stylochaeton clade (Zamioculcadoideae s.lat.)

3/26. Tropical, with the highest diversity in tropical Africa. Rhizomatous geophytes. Sterile flowers often present between female and male floral zones in inflorescence, developing in various ways. Tepals present. Stamens usually free (sometimes connate). Anthers introrse to extrorse (in Zamioculcas introrse). Pollen grains large, often with encircling sulcus. Columellae twisted, forming an ‘inner tectum’ together with outer tectum. Endexine lamellate. Intine thin. Pistil composed of two connate carpels. Placentation axile. Ovule one per carpel, ascending. Endosperm almost absent. Pistillodia present in male flowers. Ovules tenuinucellar. Micropyle bistomal. Nucellar cap and integumentary endothelium present. – Stylochaeton is sister to a clade consisting of Zamioculcas and Gonatopus.

Stylochaeton

1/20. Stylochaeton (20; central and eastern tropical Africa to Angola). – Biforines present. Leaves simple. Tepals connate. Pollen grains inaperturate. Sporopollenin ectexine very thin, undifferentiated. x = 14. – Stylochaeton resembles Zamioculcadoideae in its floral morphology. However, pollen and leaf morphology correspond well with main stream Araceae.

Zamioculcadoideae Bogner et Hesse in Aroideana 28: 13. Jul 2005

2/6. Zamioculcas (1; Z. zamiifolia; southeastern tropical Africa), Gonatopus (5; G. angustus, G. boivinii, G. clavatus, G. marattioides, G. petiolulatus; tropical East and southeastern Africa). – Kenya to northeastern South Africa. Stem condensed, thickened. Biforines absent. Leaves pinnately compound. Pseudopetiole geniculate. Pollen grains zonasulcate (extended-monosulcate). x = 17. –The pollen grains in Lasioideae, with a lamellate endexine, are relatively similar to those in Zamioculcadoideae.

Aroideae Arn., Botany: 136. 9 Mar 1832 [‘Arineae’], sensu lato

79/1.900–1.935. Tropical and subtropical regions on both hemispheres, temperate regions in Europe and eastern North America. Collenchyma usually in cortical bands or in bundle-associated strands, or absent. Laticifers usually present (simple and articulated or anastomosing; sometimes absent). Biforines often present; biforine walls thick, lignified, papillate at ends, with mucilaginous cell cytoplasm. Leaves spiral. Spatha differentiated into tube and lamina. Tepals absent. Filaments usually connate (rarely free). Anthers usually extrorse (sometimes introrse), longicidal (sometimes poricidal), with thick connectives. Pollen grains usually bicellular (sometimes tricellular) at dispersal. Exine with various sculpturing. Ectexine thin, usually without sporopollenin (consisting of polysaccharides). Endexine thick, spongy. Intine massive. Female flowers usually with staminodia. Stylodia usually free (sometimes connate). Male flowers usually with pistillodium. Placentation apical, basal or parietal. Ovules one to numerous per carpel, usually orthotropous, usually tenuinucellar (in Calla crassinucellar). Outer integument four to ten cell layers thick. Endosperm present, often starchy, or absent. Embryo sometimes chlorophyllous. Collar rhizoids sometimes present.

Callopsideae Engl. in Engler et Prantl, Nat. Pflanzenfam. Nachtr. 2: 29, 34. Apr 1906

1/1. Callopsis (1; C. volkensii; Tanzania). – Callopsis may be sister to the remaining Aroideae.

Anubiadeae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 147. 1876

1/8. Anubias (8; tropical West and Central Africa). – Aquatic or semi-aquatic herbs. Exine smooth. – Anubias may be successive sister to the remaining Aroideae except Callopsis.

Montrichardieae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 144. 1876

1/2. Montrichardia (2; M. arborescens, M. linifera; southern Mexico, Central America, the West Indies, tropical South America to Peru and Brazil). – Helophytic herbs. Exine smooth. – Montrichardia may be sister to the remaining Aroideae s.lat. except Callopsideae and Anubiadeae. A fossil species, M. aquatica, has been described from Paleocene layers in Colombia.

Aroideae sensu stricto

76/1.890–1.925. Tropical and warm-temperate. Usually monoecious (sometimes dioecious; in Calla bisexual). Leaves very variable. Pollen grains inaperturate. Cotyledons sometimes nutrient storing. – Zantedeschieae are sister-group to the remainder (Philonotieae).

Zantedeschieae Engl. in Engler et Prantl, Nat. Pflanzenfam. II, 3: 113, 136. Aug 1887

24/770–775. Exine often smooth. – The basal branching of Zantedeschieae is unresolved.

The Anchomanes clade

5/36. Aglaonemateae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 148. 1876. [‘Aglaonemeae’] Aglaonema (21; tropical Asia), Aglaodorum (1; A. griffithii; West Malesia). – Nephthytideae Engl. in Engler et Prantl, Nat. Pflanzenfam. II, 3: 112, 128. Aug 1887. Nephthytis (6; N. afzelii, N. bintuluensis, N. hallaei, N. mayombensis, N. poissonii, N. swalnei; tropical West and Central Africa, one species, N. bintuluensis, on Borneo), Pseudohydrosme (2; P. buettneri, P. gabunensis; Gabon), Anchomanes (6; A. abbreviatus, A. boehmii, A. dalzielii, A. difformis, A. giganteus, A. nigritianus; tropical Africa). – Tropical Africa, tropical Asia. Foliar collenchyma usually Type Sb. Spatha boat-shaped, early caducous or marcescent. Nephthytideae are characterized by very strongly developed basal foliar ribs, having dracontioid lobing.

Homalomeneae (Schott) M. Hotta in Mem. Fac. Sci. Kyoto Univ., ser. Biol., 4: 89. 1970

5/645–650. Culcasieae Engl. in Engler et Prantl, Nat. Pflanzenfam. II, 3: 112, 116. Aug 1887. Culcasia (27; tropical Africa), Cercestis (10; tropical West and Central Africa). – Philodendreae Schott, Syn. Aroid.: 71. Mar 1856. Philodendron (c 490; Florida, southern Mexico, Central America, the West Indies, tropical South America), Adelonema (16; tropical America), Homalomena (100–105; tropical Asia, tropical America). – Pantropical. Roots with sclerotic hypodermis and resin canals. Anthers usually without endothecial thickenings (present in Homalomena). – Culcasieae are hemiepiphytic climbing plants. Philodendreae are characterized by female-sterile-male spadix floral zonation. Thaumatophyllum (tropical South America; in Philodendron s.l.) is sometimes recovered as sister-group to Philodendron s.str. (Vasconcelos & al. 2018, Sakuragui & al. 2018).

The Zantedeschia clade sensu stricto

14/88–90. Zantedeschiaclade Zantedeschia (8; eastern tropical and southern Africa). – Spathicarpeae Schott, Syn. Aroid.: 214. Mar 1856. Lorenzia (1; L. umbrosa; Amapá in northern Brazil), Bognera (1; B. recondita; Brazil), Gearum (1; G. brasiliense; central Brazil), Dieffenbachia (c 55; southern Mexico, Central America, the West Indies, tropical South America), Mangonia (2; M. tweedieana, M. uruguaya; Brazil, Uruguay), Incarum (1; I. pavonii; Ecuador, Peru, Bolivia), Gorgonidium (8; Peru, Bolivia, northern Argentina), Spathantheum (2; S. fallax, S. orbignyanum; the Andes in Peru, Bolivia and northern Argentina), Synandrospadix (1; S. vermitoxicus; Bolivia, northern Argentina), Croatiella (1; C. integrifolium; Ecuador), Spathicarpa (3; S. gardneri, S. hastifolia, S. lanceolata; southern tropical South America), Taccarum (6; T. caudatum, T. crassispathum, T peregrinum, T. ulei, T. warmingii, T. weddellianum; tropical South America), Asterostigma (8; Brazil). – Tropical and southern Africa, tropical America. Spathicarpeae are characterized by connate stamens and x = 17.

Philonotieae S. Y. Wong et P. C. Boyce in S. Y. Wong et al., Taxon 59: 121. 5 Feb 2010

52/1.120–1.150. Calla is sometimes recovered as sister to the Dracunculus clade, although with weak support (Cusimano & al. 2011), and sometimes as sister to the clade [Rheophytes clade+Dracunculeae] (Henriquez & al. 2014).

Calleae Bartl., Ord. Nat. Plant.: 67. Sep 1830 [‘Callea’]

1/1. Calla (C. palustris; temperate regions on the Northern Hemisphere). – Rooted helophytic herb. Bisexual. Vascular bundles amphivasal. Simple articulated laticifers present. Biforines absent. Leaves distichous. Leaf sheath elongate, ligulate. Tepals absent. Pollen grains diporate. Pistil composed of a single carpel. Placentation basal. Ovules six to nine per carpel, crassinucellar. Endosperm present. Embryo with chlorophyll. Seedling roots with chlorophyll. n = 18, 27. – The bisexual flowers are remarkable, yet may be due to a reversal.

The Rheophytes clade (sensu Cabrera & al. 2008)

15/255–265. Philonotion clade Philonotion (1; P. spruceanum; northernmost South America). – Cryptocoryneae Blume, Rumphia 1: 83. Jul-Nov 1836. Lagenandra (15; southern India, Sri Lanka, Assam, Bangladesh), Cryptocoryne (65; India and Sri Lanka to southern China and Southeast Asia, Malesia to New Guinea). – Schismatoglottideae Nakai, Chosakuronbun Mokuroku [Ord. Fam. Trib. Nov.]: 218. 20 Jul 1943. Piptospatha (12; peninsular Thailand, the Malay Peninsula, Borneo), Ooia (2; O. grabowskii, O. kinabaluensis; Borneo), Pichinia (1; P. disticha; Sarawak), Schottarum (2; S. josefii, S. sarikeensis; Kanowit-Song-Ai area in Sarawak), Phymatarum (1; P. borneense; Borneo), Schismatoglottis (100–110; southern China, Southeast Asia, Malesia to Solomon Islands and Vanuatu, Taiwan, with their highest diversity on Borneo), Aridarum (10; Borneo), Schottariella (1; S. mirifica; Borneo), Bucephalandra (30; Borneo), Bakoa (1; B. lucens; Sarawak), Apoballis (12; Thailand, West Malesia, Timor), Hestia (1; H. longifolia; Sarawak). – Northernmost South America, tropical Asia, with their highest diversity on Borneo. Mainly aquatics and rheophytes. Anthers with horned thecae. Exine often smooth. – The Rheophytes clade corresponds to Schismatoglottideae sensu lato, with the addition of Philonotion. Cryptocoryneae are characterized by absence of laticifers, foliar Type Sv collenchyma, presence of squamulae intravaginales, spatha and spadix forming two chambers by partial fusion, spatha with internal flap and connate margins, and n = 18. Schismatoglottideae have erect aerial stems, early caducous or marcescent upper pseudolamina, leaf sheath with long ligules at apex, and spatha with persistent basal half.

Dracunculeae Schott in Schott et Endlicher, Melet. Bot.: 16. 1832 [‘Dracunculinae’]

36/865–885. Foliar collenchyma Type Sv. Sympodial inframarginal vein usually present on each side of pseudolamina. Exine usually spinulate. Stamens often more or less connate into a synandrium. – Amorphophalleae are sister-group to the remaining Dracunculeae.

Amorphophalleae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 144. 1876

12/c 410. Thomsonieae Blume in Rumphia 1: 138. Apr-Jun 1837. Amorphophallus (c 200; tropical regions in the Old World). – Caladieae Schott in Schott et Endlicher, Melet. Bot.: 18. 1832. Jasarum (1; J. steyermarkii; Venezuela, Guyana), Hapaline (8; Burma to Borneo), Caladium (14; Costa Rica, Panamá, tropical South America), Syngonium (c 35; Florida, Mexico, Central America, the West Indies, tropical ), Filarum (1; F. manserichense; Peru), Ulearum (2; U. donburnsii, U. sagittatum; Amazonia in Brazil), Xanthosoma (c 75; Mexico, Central America, the West Indies, tropical South America), Chlorospatha (c 70; Costa Rica, Panamá, tropical South America, with the largest diversity in the northwestern Andes), Scaphispatha (1; S. gracilis; Bolivia), Zomicarpella (2; Z. amazonica: northwestern Brazil; Z. maculata: Colombia, Peru), Zomicarpa (2; Z. pythonium, Z. steigeriana; northeastern Brazil). – Pantropical. Thomsonieae have tripartite primary leaf development with decompound subdivision, involute ptyxis, often no sterile zone between the male and female zones, and presence of smooth or staminodial spadix appendix. Caladieae are characterized by anastomosing laticifers, persistent spathe tube, and early caducous or marcescent spathe lamina.

Ambrosineae Schott in Schott et Endlicher, Melet. Bot.: 16. 1832 [‘Ambrosinieae’]

24/455–475. The Colletogyne clade is sister to Pistieae.

The Colletogyne clade

7/19. Arisareae Dumort., Fl. Belg.: 162. 1827. Arisarum (3; A. proboscideum, A. simorrhinum, A. vulgare; Macaronesia except Cape Verde Islands, the Mediterranean to the Caucasus), Ambrosina (1; A. bassii; central Mediterranean). – Typhonodoreae Engl. in Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 39: 146. 1876. Peltandrinae Schott, Syn. Aroid.: 50. Mar 1856. Peltandra (2; P. sagittifolia: southeastern United States; P. virginica: southeastern Canada, eastern and southeastern United States, Cuba), Typhonodorum (1; T. lindleyanum; coastal regions in East Africa, Madagascar, the Mascarene Islands). – Arophyteae A. Lemee ex Bogner in Bot. Jahrb. Syst. 92: 9. 1972. Arophyton (7; A. buchetii, A. crassifolium, A. humbertii, A. pedatum, A. rhizomatosum, A. simplex, A. tripartitum; Madagascar), Carlephyton (3; C. diegonse, C. glaucophyllum, C. madagascariense; northern Madagascar), Colletogyne (1; C. perrieri; Madagascar). – The Mediterranean to the Caucasus, Macaronesia, East Africa, Madagascar, the Mascarene Islands, North America. Arisareae are characterized by striate exine, connate spathe margin, and adnation of the spadix female zone to spathe. Typhonodoreae have staminodia in female zone, endosperm sparse to absent, embryo large, and cotyledon nutrient-storing. Peltandrinae are helophytes with parallel-pinnate fine venation, spathae with a persistent tube and caducous or marcescent lamina, female-sterile-male-sterile zonation of spadix, staminodial spadix appendices, and entirely connate stamens. Arophyteae, in Madagascar, have female-male zonation of spadix, connate stamens, globose pollen grains, and spinulate exine.

Pistieae Lecoq et Juill., Dict. Rais. Term. Bot.: 56, 493. 1831 [‘Pistiaceae’]

17/435–440. Protarumclade Protarum (1; P. sechellarum; the Seychelles). – Pistia clade Pistia (1; P. stratiotes; tropical East Africa?). – Colocasieae Brongn., Enum. Plant. Mus. Paris: 13. 12 Aug 1843. Ariopsis (2; A. peltata: Western Ghats, Sikkim, Assam; A. protanthera: Bhutan, Burma), Steudnera (8; the Himalayas, Southeast Asia to the Malay Peninsula), Remusatia (4; R. hookerana, R. pumila, R. vivipara, R. yunnanensis; tropical Africa, Madagascar, India, Sri Lanka, the Himalayas, Tibet, Burma, southern China, Southeast Asia, Malesia to tropical Australia, Taiwan and islands in the Pacific), Colocasia (10; the Himalayas, Tibet, Burma, southern China, Southeast Asia, the Nicobar Islands, West Malesia). – Englerarum (1; E. hypnosum; southwestern Yunnan, Laos, Thailand). – Alocasiinae Schott, Syn. Aroid.: 43. Mar 1856 [‘Alocasinae’]. Alocasia (c 80; the Hmalayas and southeastern China to Southeast Asia, Malesia to New Guinea and tropical Australia); Arisaema (180–185; eastern Africa, southern Arabian Peninsula, India, the Himalayas, Tibet, East and tropical Asia to New Guinea, southeastern Canada, eastern and southeastern United States, Mexico); Pinellia (9; China, the Korean Peninsula, Japan, the Ryukyu Islands). – Areae Theriophonum (7; T. dalzellii, T. danielii, T. fischeri, T. infaustum, T. manickamii, T. minutum, T. sivaganganum; central and southern India, Sri Lanka), Typhonium (c 70; Mongolia, China, tropical Asia to New Guinea and tropical Australia, Taiwan), Eminium (9; eastern Mediterranean to Iran, Afghanistan and Central Asia), Biarum (21; the Mediterranean from Morocco to Syria and Egypt), Arum (c 30; Europe, the Mediterranean to Iran and the Himalayas), Dracunculus (3; D. canariensis: the Canary Islands, Madeira; D. muscivorus: Corsica, Sardinia, the Balearic Islands; D. vulgaris: central and eastern Mediterranean). – Europe, Macaronesia, the Mediterranean, tropical Africa, Madagascar, the Arabian Peninsula, western and Central Asia, East and tropical Asia to tropical Asia and islands in the Pacific, eastern North America. Pistia has exostomal ovules. Colocasieae have peltate leaves, usually anastomosing laticifers, colocasioid fine leaf venation, and entirely connate stamens. Areae are a subclade within the clade Alocasiinae and are characterized by reticulate fine leaf venation, usually smooth spadix appendices, spinulate exine, bristle- or hair-like staminodia (together with Arisaema), and orthotropous ovules.

Bayesian summary tree of Araceae based on DNA sequence data (Cabrera & al. 2008). Gymnostachys is identified in some other analyses as sister to the remaining Araceae. In many analyses Lasioideae are sister-group to the Zamioculcadoideae clade plus the rest; this alternative is followed in the text above.

Bayesian summary tree of Orontioideae based on DNA sequence data (Cabrera & al. 2008).

Bayesian summary tree of Lemnoideae based on DNA sequence data (Rothwell & al. 2004; Cabrera & al. 2008).

Bayesian summary tree of Pothoideae based on DNA sequence data (Cabrera & al. 2008).

Bayesian summary tree of Monsteroideae based on DNA sequence data (Cabrera & al. 2008).

Bayesian summary tree of Lasioideae based on DNA sequence data (Cabrera & al. 2008).

Bayesian summary tree of Aroideae sensu stricto based on DNA sequence data (Cabrera & al. 2008).

Butomineae Engl., Syllabus, ed. 2: 73. Mai 1898; Butomales Rich. in C. F. P. von Martius, Consp. Regn. Veg.: 8. Sep-Oct 1835 [‘Butomeae’]; Butomanae Takht. ex Reveal in Novon 2: 235. 13 Oct 1992

Fossils Seeds that may be attributed to Butomaceae have been described from the Oligocene onwards in Europe.

Habit Bisexual, perennial herb. Aquatic or helophytic. Axillary buds sometimes developing into short-stalked bulbils. Rhizome starchy and with monopodial branching.

Vegetative anatomy Roots sometimes contractile. Phellogen absent. Secondary lateral growth absent. Endodermis absent. Vessels present in roots. Vessel elements with usually simple (sometimes scalariform) perforation plates; lateral pits? Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes multilacunar with several leaf traces. Schizogenous secretory canals absent; laticifers absent. Outer part of rhizome cortex with crystals as irregular polygonal groups or single styloids.

Leaves Alternate (distichous), simple, entire, linear, triangular in cross-section, not differentiated into pseudopetiole and pseudolamina, with ? ptyxis. Stipules absent; leaf sheath well developed. Leaf base with a row of intravaginal hairlike scales, squamulae intravaginales. Venation parallelodromous. Stomata paracytic. Cuticular wax crystalloids non-orientated. Schizogenous secretory canals and cavities. Mesophyll cells often with calciumoxalate crystals. Leaf margin entire.

Inflorescence Terminal, umbel-like, cymose, on a long peduncle (scape) from rhizome, subtended by usually three (sometimes two or four) spathe-like bracts. Floral bracts sometimes absent.

Flowers Actinomorphic. Hypogyny. Tepals 3+3, free; outer tepals petaloid-sepaloid, with imbricate aestivation; inner tepals petaloid, crumpled in bud, caducous. Gynoecial-septal nectaries present on lateral walls of carpel bases. Disc absent.

Androecium Stamens 6+3 (outer stamens paired, bifid?, alternipetalous, alternating with inner stamens). Filaments flat, free from each other and from tepals. Anthers basifixed, non-versatile, tetrasporangiate, latrorse, longicidal (dehiscing by longitudinal slits). Corolla/androecium-primordia with one pair of stamens probably first differentiating and subsequently one adaxial stamen. Tapetum amoeboid-periplasmodial, with uninucleate cells. Staminodia absent.

Pollen grains Microsporogenesis successive. Pollen grains monosulcate, shed as monads, tricellular at dispersal. Exine semitectate, with columellate infratectum, reticulate, smooth.

Gynoecium Carpels six, in one whorl, usually at best postgenitally fused; carpel plicate or conduplicate, incompletely closed at apex (carpellary margins held together distally by interwoven hairs). Stylodia very short. Stigmatic surfaces ventral, more or less decurrent, bilobate, papillate, Dry type. Pistillodia absent.

Ovules Placentation laminar-diffuse (lateral, ovules scattered over carpellary surface); placentae covered with secretions. Ovules c. 20 to more than 100 per carpel, anatropous, bitegmic, crassinucellar. Micropyle ?-stomal. Outer integument ? cell layers thick. Inner integument ? cell layers thick. Parietal cell formed from archesporial cell. Parietal tissue one cell layer thick. Megagametophyte monosporous, Polygonum type. Synergids with a filiform apparatus. Antipodal cells not proliferating. Endosperm development helobial. Endosperm haustoria? Embryogenesis caryophyllad.

Seeds Aril absent. Seed coat testal-tegmic. Exotesta with thickened epidermal cell walls and with incrustations. Endotesta? Tegmen persistent. Perisperm not developed. Endosperm absent. Embryo large, straight, well differentiated, starchy, without chlorophyll. Cotyledon one. Cotyledon hyperphyll elongate, assimilating. Hypocotyl internode long. Coleoptile absent. Germination phanerocotylar.

Cytology n = (7) 8, 10–15, 20, 21 – Triploid individuals with 2n = 39 are frequent in Europe. Chromosomes 3,7–8,3 μm long.

Phytochemistry Flavone-C-glycosides present. Flavonols, ellagic acid, proanthocyanidins, alkaloids, saponins, and cyanogenic compounds not found.

Cymodoceales Nakai, Chosakuronbun Mokuroku [Ord. Fam. Trib. Nov.]: 211. 20 Jul 1943

Distribution Mainly tropical and subtropical coastal marine areas; some species in warm-temperate seas along coasts of Australia and the Mediterranean.

Fossils Thalassocharis was described from the late Cretaceous in the Netherlands, and Thalassodendron auricula-leporis from the Mid-Eocene of Florida, USA. These may be assigned to Cymodoceaceae. Furthermore, Cymodocea is known from several Cenozoic fossils.

Habit Monoecious or dioecious, perennial herbs. Marine. Submersed. Rhizome in Cymodocea, Halodule and Syringodium herbaceous, monopodially branched, in Amphibolis and Thalassodendron lignified, sympodially branched.

Vegetative anatomy Mycorrhiza absent. Roots often with bacterial colonies (nitrogen-fixing?). Epidermal cells of roots usually lignified. Phellogen absent. Endodermal and some outer-cortical and epidermal cell walls of rhizome lignified. Secondary lateral growth absent. Vessels absent (also in roots). Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve elements in Halodule with thick nacreous cell walls (absent from roots). Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Tanniniferous cells abundant. Calciumoxalate crystals absent.

Leaves Alternate (distichous), simple, entire, linear to terete, with ? ptyxis. Stipules absent; leaf sheath well developed, with basal membranous sheath-like ligule in transition zone to lamina; axillary intravaginal scales, squamulae intravaginales, two or more. Venation parallelodromous; primary veins connected by transversal veins. Stomata absent. Cuticular wax absent. Mesophyll without calciumoxalate crystals. Epidermis with tanniniferous cells. Leaf margin subentire, at apex finely serrate.

Inflorescence Flowers axillary, usually solitary (in Syringodium in few-flowered cymose inflorescences), surrounded by a spatha (bract).

Flowers Zygomorphic?, small. Tepals absent? (in Amphibolis transformed into an attachment organ). Nectary absent. Disc absent.

Androecium Stamens two. Filaments connate. Anthers somewhat twisted, connate into a synandrium, basifixed, non-versatile, tetrasporangiate, longicidal (dehiscing by longitudinal slits); connective in Amphibolis and Thalassodendron with two or three apical appendages on each lobe. Tapetum amoeboid-periplasmodial, with uninucleate cells. Staminodia absent.

Pollen grains Microsporogenesis usually successive (in Thalassodendron simultaneous). Pollen grains inaperturate, filiform (in Amphibolis up to 5 mm long), in anthers spirally twisted, shed as monads, tricellular at dispersal. Exine absent; pollen surface usually with pitted longitudinal ridges.

Gynoecium Carpels two, free (apocarpy); usually only one carpel developing into fruit. Ovary unilocular. Stylodia long, simple (in Halodule) or bilobate (bibrachiate) or trilobate (tribrachiate; in Amphibolis). Stigmas long, narrow, Dry type. Pistillodium absent?

Ovules Placentation apical (Syringodium) or basal (Thalassodendron). Ovule one per carpel, anatropous (Syringodium, Thalassodendron) or orthotropous (Syringodium), pendulous, bitegmic, crassinucellar. Micropyle ?-stomal. Outer integument ? cell layers thick. Inner integument ? cell layers thick. Parietal cell? Megagametophyte monosporous, Polygonum type? Endosperm development ab initio nuclear. Endosperm haustoria? Embryogenesis? In Amphibolis an attachment structure with four hardening fleshy pericarp lobes with bristle hairs formed from ovary wall.

Fruit Nutlike or drupaceous (Cymodocea, Halodule, Syringodium; in Thalassodendron a pseudofruit with innermost bracts enclosing carpels during fruit stage).

Seeds Aril absent. Testa present in Cymodocea, Halodule, and Syringodium, absent in Amphibolis and Thalassodendron. Tegmen? Perisperm not developed? Endosperm absent. Embryo large, straight? (macropodous), well differentiated, chlorophyll? Cotyledon usually one. Hypocotyl in Cymodocea, Halodule and Syringodium large, rich in starch. Amphibolis, Thalassodendron and Cymodocea antarctica viviparous, often with small or no cotyledon, but with transfer cells between embryo and mother tissue.

Phytochemistry Insufficiently known. Polyphenols, phenolic sulphates (sulphonated phenolic acids), proanthocyanidins and cyclitols (cyclic polyols) present.

Najadaceae Juss., Gen. Plant.: 18. 4 Aug 1789 [’Naiades’], nom. cons.; Najadopsida Hoffmanns. et Link, Fl. Portug. 1: 59. 1 Sep 1809 [’Naïdes’]; Hydrocharitales Juss. ex Bercht. et J. Presl, Přir. Rostlin: 271. Jan-Apr 1820 [‘Hydrocharideae’]; Najadales Bercht. et J. Presl, Přir. Rostlin: 271. Jan-Apr 1820 [‘Najadeae’]; Elodeaceae Dumort., Anal. Fam. Plant.: 54. 1829; Vallisneriaceae (Dumort.) Dumort., Anal. Fam. Plant.: 54, 55. 1829; Hydrocharitopsida Bartl., Ord. Nat. Plant.: 25, 74. Sep 1830 [’Hydrocharideae’]; Stratiotaceae Schultz Sch., Nat. Syst. Pflanzenr.: 274. 30 Jan-10 Feb 1832 [’Stratioteae’]; Halophilaceae J. Agardh, Theoria Syst. Plant.: 50. Apr-Sep 1858 [’Halophileae’]; Otteliaceae Chatin in Casp., Jahrb. Wiss. Bot. 1: 482. 1858, nom. illeg.; Hydrillaceae Prantl, Lehrb. Bot., ed. 3: 188. 24 Jan 1879 [’Hydrilleae’]; Enhalaceae Nakai, Chosakuronbun Mokuroku [Ord. Fam. Trib. Nov.]: 210, 211. 20 Jul 1943; Thalassiaceae Nakai, Chosakuronbun Mokuroku [Ord. Fam. Trib. Nov.]: 210. 20 Jul 1943; Blyxaceae (Aschers. et Gürcke) Nakai in J. Jap. Bot. 24: 14. Dec 1949; Vallisneriales Nakai in J. Jap. Bot. 24: 14. Dec 1949; Elodeales Nakai in J. Jap. Bot. 25: 5. Feb 1950; Najadanae Takht. ex Reveal in Novon 2: 236. 13 Oct 1992

Distribution Mainly in tropical and subtropical but also temperate regions: Eurasia, Australia, North America, coastal marine areas in the West Indies, and the Indian Ocean to the Pacific.

Fossils Stratiotes is known from a large number of fossil seeds from the Late Paleocene and onwards. Fossil Hydrocharis has been found in Neogene layers of Germany och Switzerland. Fossil seeds of Najas and Najadites are known from the Oligocene of England and Russia. The extinct genus Ceratostratiotes from the early Miocene of northern Austria resembles Blyxa, but should perhaps be assigned to Ceratophyllaceae.

Habit Usually monoecious, polygamomonoecious, or dioecious (sometimes bisexual), usually perennial (sometimes annual) herbs. Aquatic, often submersed. Some genera are growing in salt or brackish water. Roots usually unbranched (in Najas fibrous). Stems monomorphic, dimorphic or polymorphic.

Vegetative anatomy Mycorrhiza absent in marine species. Root epidermis in Hydrocharis arising from inner epidermis. Phellogen absent. Secondary lateral growth absent. Endodermis indistinct or thick-walled. Vessels usually absent (present in roots of some species). Vessel elements with scalariform perforation plates; lateral pits? Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Laticifers and schizogenous secretory canals absent. Calciumoxalate crystals and silica bodies absent. Hydrilla, Egeria, etc. have C₄ photosynthesis in specialized cells.

Leaves Usually alternate (sometimes distichous; rarely verticillate; in Najas seemingly opposite, although in reality alternate and distichous), simple, entire, often differentiated into pseudopetiole and pseudolamina, often linear, sometimes scale-like (consisting of a mere leaf sheath), with supervolute (involute) or convolute ptyxis. Stipules membranous, single median or paired lateral, or absent; leaf sheath well developed or absent. Pseudopetiole sometimes with wings or spines. Intravaginal scales, squamulae intravaginales, (one or) two to more than ten, mucilaginous? Venation parallelodromous or acrodromous; often with transversal veins. Some species with inverted vascular bundles. Stomata usually absent (paracytic when present). Cuticular wax absent. Leaf margin serrate (sometimes serrate-dentate), dentate or entire. Leaf apex in Najas with one to three unicellular or multicellular teeth on each side.

Inflorescence Terminal or axillary, cymose of various shape (often umbel-like panicles), or flowers solitary (female flowers often solitary), with one or two free or connate spathe-like bracts (flowers in Najas solitary or few together, axillary; each female flower surrounded by one and each male flower by two membranous scale-like bracts). Floral prophyll (bracteole) varying in number and position (sometimes lateral or pairwise).

Flowers Usually actinomorphic (in some genera zygomorphic as young), often small; male flowers in some genera detached from plant immediately prior to anthesis; bisexual flowers often cleistogamous. Hypanthium present in female flowers in some genera. Epigyny. Outer tepals three, sepaloid, with valvate aestivation, caducous or persistent, free (absent in Najas); inner tepals usually three (rarely fewer than three or absent), petaloid, thin, crumpled in bud, caducous, free. Nectaries at stylodial bases usually three, probably staminodial in origin (rarely more than three; sometimes absent). Disc absent.

Androecium Stamens (one to) three or 3+3 (sometimes up to six [to ten] whorls, each one with three stamens, antesepalous stamens sometimes paired; in Najas a single stamen). Filaments (branched? or) simple, free from each other and from tepals. Anthers basifixed or dorsifixed, non-versatile?, usually tetrasporangiate (in Enhalus and Halophila disporangiate; in some species of Najas monosporangiate), introrse, latrorse or extrorse, longicidal (usually dehiscing by longitudinal slits; in Najas with a short apical slit), sometimes connate. Tapetum amoeboid-periplasmodial, with uninucleate cells. Staminodia very varying in number, shape and function, extrastaminal or intrastaminal (absent in Najas).

Pollen grains Microsporogenesis successive. Pollen grains inaperturate, usually shed as monads (in Elodea often as tetrads; in Halophila and Thalassia filiform, cohering in moniliform chain-like bands covered by mucilage), usually tricellular (sometimes bicellular) at dispersal. Exine semitectate to intectate, often very thin, with columellate infratectum, psilate, verrucate, echinate or spinulate, sometimes confined to scattered columellae and spinules (absent in some species). Pollen grains at least in Najas with starch grains.

Gynoecium Pistil composed of (one to) three to six (to more than 20) usually partially connate (sometimes free?) carpels (in Elodea antepetalous); carpel plicate (sometimes ascidiate at base), occluded by secretion only. Ovary inferior, unilocular (often seemingly septate by intrusion of free carpellary margins; ovary wall in Najas two cell layers thick), sometimes filled with mucilage (from mucilaginous hairs?). Style single, or stylodia three to more than 20, sometimes connate at base. Stigmas filiform, branched, papillate (with multicellular papillae), Dry type. Male flowers often with usually trilobate pistillodia (lobes often split).

Ovules Placentation usually parietal to laminal (in, e.g., Najas basal), often strongly intrusive. Ovules one or few to more than 100 per carpel, usually anatropous (sometimes orthotropous, rarely amphitropous), ascending to pendulous, bitegmic, crassinucellar or pseudocrassinucellar. Micropyle usually bistomal (in, e.g., Najas endostomal). Outer integument often three or more cell layers thick. Inner integument ? cell layers thick. Parietal cell formed from archesporial cell. Parietal tissue one or two cell layers thick. Nucellar cap usually three cell layers thick. Megagametophyte monosporous, Polygonum type. Synergids sometimes with a filiform apparatus. Antipodal cells not proliferating. Endosperm development usually helobial (in Najas nuclear). Endosperm haustorium chalazal. Embryogenesis caryophyllad.

Fruit A berry or a capsule (sometimes fleshy; in Najas a nutlike fruit, with gradually decaying wall).

Seeds Aril absent. Seed coat testal. Exotesta present. Mesotesta and endotesta often with stone cells. Testal cell walls often thickened. Endotegmic cell walls with unique small tubercles, with only tuberculate inner wall persistent. Perisperm not developed. Starch present. Endosperm usually absent (in Ottelia sparse). Suspensor haustorium unicellular. Embryo large (often macropodous), usually straight, little or well differentiated, usually without chlorophyll (in Najas with chlorophyll). Cotyledon one, bifacial; embryo at germination often with several leaves; hypocotyl massive often with unicellular attachment hairs. Cotyledon hyperphyll elongate, assimilating. Hypocotyl internode well developed. Coleoptile absent. Radicula absent in, e.g., Stratiotes. Germination phanerocotylar. Synergid polyembryony known from several species of Najas.

Cytology n = 6–66 – Polyploidy and aneuploidy frequently occurring. Chromosomes (0,8–)1,6–11,7 μm long.

DNA Significant losses of mitochondrial genes; introne 2 in the mitochondrial gene nad1 is absent in at least some species.

Phytochemistry Flavones, flavone-C-glycosides, flavone sulphates, cyanidin, 5-methylcyanidin (in Egeria) caffeic acid derivatives, cyanine and polyphenolic glycosides, chlorogenic acids, phenolic sulphates, and hemicellulose-bound apiose present. Cell wall bound ferulate absent in unlignified cell walls. Flavonols, ellagic acid, alkaloids, and saponins not found.

Use Ornamental plants, aquarium plants, vegetables (e.g. Ottelia cordata).

Systematics Hydrocharitaceae are sister-group to Butomus (Butomaceae). The following classification is in accordance with Les & al. (2006). A possible topology is: [Hydrocharitoideae+[Stratiotoideae+[Anacharidoideae+[Najadeae+[Halophileae+Vallisnerieae]]]]].

Hydrocharitoideae Eaton, Bot. Dict., ed. 4: 29, 44. Apr-Mai 1836 [‘Hydrocharides’, ‘Hydrocharideae’]

2/4. Hydrocharis (3; H. morsus-ranae: Europe, North Africa, the Caucasus, Central Asia, Siberia; H. chevalieri: tropical West and Central Africa; H. dubia: East and tropical Asia to the Russian Far East and New Guinea), Limnobium (1; L. spongia; southeastern United States). – Temperate and subtropical regions. Monoecious. Leaves wide, with involute or convolute ptyxis. Foliar vascular bundles inverted. Pseudopetiole present. Ligulae basal, adaxial or paired lateral, entirely enclosing young leaves. Leaf margin entire. Male flowers with three sepaloid tepals and three petaloid tepals. Female flowers with three sepaloid tepals and three or no petaloid tepals. Stamens (one or) three or 3+3. Pistil composed of three to nine connate carpels. Placentae strongly intrusive. Exotestal cells much enlarged. Exotegmic tuberculae present. n = 7, 8, 10, 11, 13–15. –Hydrocharitoideae are sister to the remaining Hydrocharitaceae.

[Stratiotoideae+[Anacharidoideae+[Najadeae+[Halophileae+Vallisnerieae]]]]

Stratiotoideae Luerss., Handb. Syst. Bot. 2: 309. Dec 1879 [‘Stratiotideae’]

1/1. Stratiotes (1; S. aloides; Europe, temperate Asia). – Dioecious. Roots unbranched. Leaves tristichous, spiny, in rosettes. Stamens numerous, inner five to 17 of which fertile. Female flowers with staminodia. Carpels six, free, in two whorld (outer carpels antesepalous). n = >10. – Stratiotes is sister to [Anacharidoideae+Hydrilloideae].

[Anacharidoideae+[Najadeae+[Halophileae+Vallisnerieae]]]

Anacharidoideae Thomé, Fl. Deutschl. 1: 84. 1886 [‘Anacharideae’]

7/51–52. Apalanthe (1; A. granatensis; tropical South America), Appertiella (1; A. hexandra; Madagascar), Lagarosiphon (9; tropical and southern Africa, Madagascar), Egeria (3; E. densa, E. heterostemon, E. najas; subtropical South America), Elodea (5–6; E. bifoliata, E. callitrichoides, E. canadensis, E. granatensis, E. nuttallii, E. potamogeton; Canada, the United States, South America), Blyxa (12; tropical Africa, Madagascar, tropical and subtropical Asia to tropical Australia and islands in western Pacific), Ottelia (c 20; tropical Africa, East and tropical Asia to Australia and Solomon Islands, one species, O. brasiliensis, in tropical South America). – Tropical to temperate regions on both hemispheres, with their largest diversity in North and South America. Usually dioecious (in Apalanthe and Ottelia bisexual) herbs with submerged leaves. Roots usually unbranched. Leaves distichous or pseudoverticillate. Pseudopetiole usually absent. Leaf margin finely serrate to spinose-serrate. Inflorescence axillary. Male flowers usually liberated as buds, usually with 3+3 (sometimes three) tepals. Fertile stamens three (then sometimes also three staminodia) or 3+3. Female flowers with usually long hypanthium, 3+3 tepals and staminodia. Pistil composed of three connate carpels. Placentae usually little intruded. Ovules usually few per carpel. Fruit not or irregularly dehiscent. Seeds usually fewer than 30. n = 6?, 8, 11, 12, 14, etc. – Anacharidoideae are sister-group to Hydrilloideae with low bootstrap support. In Apalanthe and species of Ottelia the flowers are bisexual. Root trichoblasts are absent in Blyxa. Blyxa has secondary pollen presentation and small chromosomes. The leaves of Ottelia have pseudopetiole and a wide lamina and the stamens are three to 15. The female flowers in Blyxa possess hypanthium, staminodia and a pistil composed of three to 20 or more connate carpels.

Hydrilloideae Luerss., Handb. Syst. Bot. 2: 308. Dec 1879 [’Hydrilleae’]

8/c 62. Tropical and subtropical regions, especially in the Old World. Roots usually unbranched. Usually dioecious herbs with submerged leaves. Pollen grains with discontinuous exine and little or no sculpturing. Pollination epi- or hypohydrophilous. Placentae usually little intruded. Ovules usually few per carpel.

[Najadeae+[Halophileae+Vallisnerieae]]

Najadeae Dumort., Fl. Belg.: 164. 1827 [‘Nayeae’]

2/c 40. Hydrilla (1; H. verticillata; temperate regions in Europe, North and East Africa, Asia and northern and eastern Australia), Najas (c 38; nearly cosmopolitan). – Subcosmopolitan. Dioecious. Root system well developed, with simple roots and numerous root hairs. Leaves more or less alternate (often seemlingly opposite), narrow. Pseudopetiole absent. Leaf base with auricle-like structure. Leaf margin serrate. Male flower with two spathae. Stamen single. Hydrophilous. Female flower with one spatha. Carpel one?, ascidiate. Style simple or bifid. Placentation basal. Ovule one. Fruit an achene? Exotegmen sometimes present. Endosperm nuclear. Embryo with chlorophyll. Cotyledon unifacial. n = 6–8. – Najas is sister to [Halophileae+Vallisnerieae] with low bootstrap support.

[Halophileae+Vallisnerieae]

Halophileae Aschers. in Flora 35: 172. Jul 1867

3/22. Enhalus (1; E. acoroides; tropical Asia to western Pacific), Thalassia (2; T. hemprichtii: the Indian Ocean, the Pacific; T. testudinum: the West Indies), Halophila (19; tropical and subtropical coastal marine waters in the Indian Ocean and the Pacific, the West Indies). – Tropical and subtropical coastal marine waters in the Indian and the Pacific Oceans, the West Indies. With rhizome and leaf-bearing short shoots. Tanniniferous cells present or absent. Leaves distichous, narrow. Leaf margin usually entire (sometimes serrate). Male flowers with tepals in two whorls, undifferentiated or three. Stamens three (to 13). Pollen grains deliberated in strands. Usually hydrophilous (not in Enhalus). Female flowers with tepals in two whorls, uniseriate or reduced. Pistil composed of three to nine connate carpels. Fruit fleshy, a capsule or irregularly dehiscent. n = ? – Halophileae are sister-group to Vallisnerieae, although with low bootstrap support. The ovary in Thalassia is elongated into a hypanthium. The lamina in Halophila is wide and has a pseudopetiole.

Vallisnerieae Dumort., Fl. Belg.: 135. 1827

3/16. Nechamandra (1; N. alternifolia; India to Southeast Asia), Vallisneria (14; tropical and subtropical regions on both hemispheres), Maidenia (1; M. rubra; northwestern Australia). – Tropical and subtropical regions on both hemispheres, with their largest diversity in the Old World. Leaves distichous or pseudoverticillate, narrow. Pseudopetiole absent. Leaf margin serrate. Inflorescence axillary. Male flowers liberated as buds, with three sepaloid tepals and (one or) no petaloid tepals. Stamens one to three; staminodium sometimes present. Female flowers with hypanthium, (two or) three sepaloid tepals and two or three petaloid tepals (sometimes absent). Female flowers with (two or) three staminodia. Pistil composed of two or three connate carpels. Fruit irregularly dehiscing. Exotegmic tuberculae sometimes present. n = 8, 10, 12, 15. – Root trichoblasts are absent in Vallisneria. In Hydrilla etc. the hypanthium is strongly elongating, while the anthers reach the water surface in small gas bubbles formed by the male flowers.

Single most parsimonious tree recovered from maximum parsimony analysis of Hydrocharitaceae based on morphological and DNA sequence data (Les & al. 2006).

Triglochinaceae Bercht. et J. Presl, Přir. Rostlin 1(7*-13): 1, 2. 1823 [’Triglochineae’]; Lilaeaceae Dumort., Anal. Fam. Plant.: 62, 65. 1829 [’Lilaearieae’], nom. cons.; Juncaginales Rich. in C. F. P. von Martius, Consp. Regn. Veg.: 6. Sep-Oct 1835 [‘Juncagineae’]; Heterostylaceae Hutch., Fam. Fl. Pl. 2: 41. 20 Jul 1934

Habit Bisexual, monoecious or polygamomonoecious (in Tetroncium dioecious), usually perennial (rarely annual) herbs. Aquatic or helophytic, in fresh or brackish water.

Vegetative anatomy Mycorrhiza absent. Roots usually fibrous (in Triglochin sometimes tuberous). Apical stem meristem usually bipartite. Phellogen absent. Secondary lateral growth absent. Endodermis present or absent. Vessel elements with scalariform perforation plates; lateral pits scalariform, simple pits. Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Laticifers present in Triglochin scilloides (‘Lilaea’). Calciumoxalate as single (prismatic?) crystals.

Leaves Alternate (usually distichous, sometimes spiral), simple, entire, linear, with ? ptyxis. Stipules absent; leaf sheath open, with two auricles (biauriculate) and numerous filiform intravaginal scales, squamulae intravaginales (in Triglochin a ligule). Venation parallelodromous. Primary vascular bundles usually with sclerenchymatous envelope, outermost layer of which often with U-shaped cell wall thickenings. Stomata paracytic or tetracytic (subsidiary cells with parallel cell divisions). Cuticular wax absent. Hypodermis in Triglochin scilloides laticiferous. Mesophyll in Triglochin sometimes with cells containing calciumoxalate as druses or single prismatic crystals. Condensed tannins sometimes present (e.g., in mesophyll cells in Triglochin scilloides). Leaf margin entire.

Inflorescence Terminal, usually spike (rarely raceme). Floral bracts usually absent (present in Triglochin scilloides).

Flowers Actinomorphic (or possibly somewhat zygomorphic), small. Hypogyny. Tepals probably absent. Nectary absent. Disc absent.

Androecium Stamens one (Triglochin scilloides), three, 2+2 or 3+3 (rarely 4+4). Filaments short, free, or absent. Anthers basifixed, non-versatile, usually tetrasporangiate (anthers in bisexual, lower, flowers of Triglochin scilloides disporangiate), extrorse, longicidal (dehiscing by longitudinal slits); connective with a tepaloid appendage, retinaculum. Tapetum amoeboid-periplasmodial, with ab initio uninucleate cells. Staminodia three or four or absent; female flowers usually with staminodia with tepaloid connective appendages.

Pollen grains Microsporogenesis successive. Pollen grains inaperturate, shed as monads, bicellular or tricellular at dispersal. Exine semitectate, with columellate infratectum, reticulate.

Gynoecium Carpels one (in bisexual flowers of Triglochin scilloides), 2+2 or 3+3 (sometimes up to ten; three carpels in Triglochin often sterile, alternipetalous), antepetalous, plicate, usually somewhat connate (rarely entirely free), separating during fruit maturation. Ovary superior, usually trilocular, quadrilocular or sexalocular (rarely unilocular, apocarpy). Stylodia usually short or absent (female flowers in some species of Triglochin with narrow style up to 3 dm). Stigmas penicillate or plumose, papillate, Dry type. Pistillodia (as sterile carpels) present in Triglochin.

Ovules Placentation usually basal. Ovules one or few per carpel, usually anatropous, usually ascending, bitegmic, crassinucellar. Micropyle ?-stomal. Outer integument three or more cell layers thick. Inner integument ? cell layers thick. Parietal cell formed from archesporial cell. Parietal tissue four to six cell layers thick. Megagametophyte monosporous, Polygonum type. Antipodal cells in Triglochin proliferating. Endosperm development ab initio nuclear. Endosperm haustoria? Embryogenesis caryophyllad.

Fruit Usually an assemblage of nutlets (in Triglochin scilloides three-winged or hooked) or follicles (in Triglochin a schizocarp with four or six nutlike mericarps).

Seeds Aril absent. Seed coat exotestal-endotegmic. Exotesta and endotegmen with cuticle; remaining layers crushed. Perisperm not developed? Starch present. Endosperm absent. Suspensor absent. Embryo straight, well differentiated, with short thick ephemeral hypocotyl, chlorophyll? Cotyledon one, large. Cotyledon hyperphyll elongate, assimilating. Hypocotyl internode absent. Coleoptile absent. Germination phanerocotylar. Seedling in Triglochin with distichous leaves.

Cytology n = 6, 9, 12, 15, 16, 18, 24, 30, 48, 60 – Polyploidy occurring. Chromosomes 0,6–1,1 μm long.

Phytochemistry Flavone-C-glycosides, flavone-O-glycosides and tyrosine-derived cyanogenic glucoside (triglochinin) present. Flavonols, ellagic acid, proanthocyanidins, alkaloids, and saponins not found.

Habit Bisexual, perennial rhizomatous herb. Aquatic or hygrophilous, in fresh water.

Vegetative anatomy Roots fibrous. Apical stem meristem bipartite. Phellogen absent. Secondary lateral growth absent. Endodermis present? Vessel elements with scalariform perforation plates; lateral pits scalariform, simple pits. Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids probably P2c type. Nodes? Laticifers absent. Calciumoxalate as single crystals.

Leaves Alternate (distichous), simple, entire, triangular in transverse section, with ? ptyxis. Stipules absent; leaf sheath absent or almost so, with two auricles (biauriculate) and numerous filiform intravaginal scales, squamulae intravaginales. Venation parallelodromous. Primary vascular bundles with sclerenchymatous envelope. Stomata paracytic. Cuticular wax probably absent. Leaf margin entire.

Flowers Actinomorphic, small. Hypogyny. Tepals probably absent (or possibly two, transversal-abaxial). Nectary absent. Disc absent.

Androecium Stamens (2+2 or) 3+3. Filaments very short, free. Anthers basifixed, non-versatile, usually tetrasporangiate, extrorse, longicidal (dehiscing by longitudinal slits); connective with a tepaloid appendage, retinaculum. Tapetum amoeboid-periplasmodial, with uninucleate cells? Staminodia absent.

Pollen grains Microsporogenesis successive? Pollen grains inaperturate, shed as monads, ?-cellular at dispersal. Exine semitectate?, with columellate infratectum?, reticulate?

Gynoecium Carpels (two or three) or four, plicate, adaxially connate, with free recurved apices, fused at fruit maturation. Ovary superior, usually quadrilocular. Styluli marginal, recurved. Stigmas linear, papillate, Dry type. Pistillodia absent.

Ovules Placentation apical. Ovules one per carpel, orthotropous, pendulous, bitegmic, crassinucellar. Micropyle ?-stomal. Outer integument ? cell layers thick. Inner integument ? cell layers thick. Parietal cell formed from archesporial cell? Chalazal part of megasporangium coenocytic. Megagametophyte monosporous, Polygonum type. Endosperm development ab initio nuclear? Endosperm haustoria? Embryogenesis?

Seeds Aril absent. Exotesta and endotegmen with cuticle; remaining layers crushed. Perisperm not developed? Starch present. Endosperm absent. Embryo straight, well differentiated, with short thick hypocotyl, chlorophyll? Suspensor absent. Cotyledon one, large. Cotyledon hyperphyll elongate, assimilating. Hypocotyl internode absent. Coleoptile absent. Germination phanerocotylar?

Cauliniaceae J. Presl in Nowočeská Bibl. [Wšobecný Rostl.] 7: 1687. 1846, nom. illeg.; Posidoniales Nakai, Chosakuronbun Mokuroku [Ord. Fam. Trib. Nov.]: 211. 20 Jul 1943

Distribution Southwest European Atlantic coasts, Mediterranean coasts, and coastal waters off South Australia and Tasmania, with their highest diversity along Australian coasts.

Fossils Single ambiguous fossils which may possibly be attributed to Posidoniaceae are known from Cretaceous and Eocene layers.

Habit Usually bisexual, perennial herbs. Marine (sometimes in brackish water). Submersed. Rhizome with one scale at each node and covered by remnants of old leaf sheaths. Old foliar fibres detached from rhizomes, rolled by sea-waves into balls and washed onto beaches along Mediterranean and southern Australian coasts.

Vegetative anatomy Mycorrhiza absent. Phellogen absent. Rhizome stele with four to ten cortical vascular bundles. Secondary lateral growth absent. Vessels absent (also in roots). Imperforate tracheary xylem elements tracheids with little lignified cell walls and with simple? pits. Wood rays absent. Axial parenchyma? Cortical parenchyma with numerous tanniniferous cells and small starch grains. Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Crystals absent.

Leaves Alternate (distichous), simple, entire, linear, with ? ptyxis. Stipules absent; leaf sheath open, biauriculate, without chloroplasts, with basal membranous sheath-like ligule in transition zone to lamina, and strongly lignified fibres, long persistent after leaf has fallen; axillary intravaginal scales, squamulae intravaginales, numerous. Venation parallelodromous; transversal veins connecting? primary veins, each of these enclosed by one cell layer with lignified cell walls. Stomata absent. Cuticular wax absent. Mesophyll without calciumoxalate crystals. Tanniniferous cells frequent. Leaf margin entire or finely serrate.

Inflorescence Axillary, botryoid or panicle, with flowers in two rows in flattened and long-stalked, three- to five-flowered, branched spike-like partial inflorescences, surrounded by fibrous leaf sheaths forming spathae (bracts). Floral bracts present.

Flowers Actinomorphic, small. Hypogyny. Tepals absent. Nectary absent. Disc absent.

Androecium Stamens three. Filaments absent or nearly so. Anthers basifixed or subbasifixed, non-versatile, tetrasporangiate, extrorse, longicidal (dehiscing by longitudinal basal slits); connective wide, discoid, tepaloid and with a prolonged midvein. Tapetum amoeboid-periplasmodial? Staminodia absent.

Pollen grains Microsporogenesis successive? Pollen grains inaperturate, filiform, shed as monads, tricellular at dispersal. Exine absent. Pollen surface smooth.

Gynoecium Pistil composed of one carpel; ventral side of carpel abaxial. Ovary superior, unilocular (monomerous, monocarpellate). Style single, simple, very short, or absent. Stigma irregularly lobate, almost discoid, with cuticle, covered with secretions, type? Pistillodium absent.

Ovules Placentation apical. Ovule one per carpel, campylotropous, pendulous, bitegmic, crassinucellar, with integumentary outgrowth. Micropyle ?-stomal. Outer integument ? cell layers thick. Inner integument ? cell layers thick. Parietal cell? Megagametophyte monosporous, Polygonum type. Endosperm development helobial. Endosperm haustoria? Embryogenesis?

Seeds Aril absent. Seed coat absent. Testa and tegmen membranous, without phytomelan. Perisperm not developed. Endosperm absent. Embryo large, straight (macropodous), well differentiated, chlorophyll? Cotyledon one. Cotyledon hyperphyll? Hypocotyl internode? Coleoptile absent? Hypocotyl large, starchy. Germination?

Cytology x = 10 – Karyotype bimodal, with five pairs of larger and five pairs of smaller chromosomes.

Phytochemistry Proanthocyanidins and phenolic sulphates (sulphonated phenolic acids) present. Flavone sulphates, alkaloids and saponins not found.

Berchtold et Presl, Přir. Rostlin 1(7*-13): 1, 3. 1823 [’Potamogetinae’], nom. cons.

Zannichelliaceae Chevall., Fl. Gén. Env. Paris 2: 257. 1827 [’Zanichellieae’], nom. cons.; Potamogetonales Dumort., Anal. Fam. Plant.: 59. 1829 [‘Potamogetarieae’]; Potamogetonineae Engl., Syllabus, ed. 2: 72. Mai 1898

Fossils Fossil leaves and fruits of Potamogetonaceae are described from Cenozoic layers of Europe and Asia.

Habit Bisexual (Groenlandia, Potamogeton, and Stuckenia), or usually monoecious (Zannichellia, Pseudalthenia and Althenia; rarely dioecious), usually perennial (rarely annual) herbs, usually without tuber. Shoot apices in Potamogeton often transformed into turions. Aquatic (in fresh water, some species in brackish water). Many species are entirely submersed.

Vegetative anatomy Mycorrhiza absent? Roots fibrous, non-septate. Outer root cortex often with somewhat lignified cells. Stem apical meristem in Zannichellia bifid. Phellogen absent. Vascular tissue usually reduced. Secondary lateral growth absent. Vessels present only in roots in some species of Potamogeton. Vessel elements with scalariform perforation plates; lateral pits? Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes?, with three main bundles often entering leaf base. Tanniniferous cells frequent. Calciumoxalate crystals and silica bodies absent.

Leaves Alternate (usually distichous, sometimes spiral; in Groenlandia pseudo-opposite), simple, entire, often differentiated into pseudopetiole and pseudolamina, with involute ptyxis, often linear, sometimes scale-like. Stipules absent; leaf sheath well developed, open, sometimes auriculate, with basal membranous sheath-like ligule in transition zone to lamina, sometimes densely pressed to (adnate to?) leaf base (absent in Zannichellia); axillary intravaginal scales, squamulae intravaginales, (one or) two to more than ten. Venation parallelodromous (leaves often one-veined); main veins usually connected to transversal veins. Stomata paracytic (often with aberrant development) or absent. Cuticular wax absent. Leaf margin usually entire (rarely crenulate or finely serrulate). Leaf in Potamogeton with apical pore. Heterophylly often present (submersed leaves different from floating leaves).

Inflorescence Terminal or axillary, scapose, usually two- to many-flowered spike- or head-like (flowers rarely solitary axillary), each one surrounded by a spatha. Floral bracts usually absent. Inflorescence in Zannichellia developing sympodially.

Flowers Actinomorphic, small. Hypogyny. Tepals absent. Nectary absent. Disc absent.

Androecium Stamens one or (two to) four (Groenlandia, Potamogeton, and Stuckenia). Filaments free. Anthers basifixed, non-versatile, 1–8(–12)-sporangiate (anthers in Althenia, Pseudalthenia, and Zannichellia with one or several disporangiate units), extrorse, longicidal (dehiscing by longitudinal slits); connective usually with abaxial tepaloid appendage (absent in male flowers of Pseudalthenia and Zannichellia); stamen and tepaloid connective appendage supported by a common trace (vascular strand branch). Tapetum amoeboid-periplasmodial, usually with ab initio uninucleate (rarely binucleate) and later multinucleate cells. Female flowers with staminodia provided with tepaloid connective appendages (in Pseudalthenia and Zannichellia as a tubular structure surrounding carpels; in Althenia as three separate parts each enveloping one carpel).

Pollen grains Microsporogenesis successive. Pollen grains usually inaperturate (rarely monosulcate), shed as monads, tricellular at dispersal. Exine usually semitectate (absent in some species), with columellate infratectum, reticulate, sometimes spinulate (sometimes absent). Pollen grains of some Althenia and Zannichellia dispersed within a common gelatinous envelope.

Gynoecium Carpels (one to) four (to eight; in Groenlandia, Potamogeton, and Stuckenia usually four), usually ‘alternitepalous’, sometimes shortly stipitate (in Zannichellia with often long stipe), free; carpel plicate and ascidiate. Ovary superior, unilocular (apocarpy). Stylodia short to long or absent. Stigmas capitate (Groenlandia, Potamogeton, and Stuckenia), peltate or infundibuliform (in Althenia bilocularis with fimbriate margin), non-papillate, Dry type. Pistillodia absent.

Ovules Placentation ventral-marginal, lateral or apical. Ovule one per carpel, orthotropous (Groenlandia, Potamogeton, and Stuckenia) or campylotropous to anatropous, pendulous, apotropous, bitegmic, crassinucellar. Micropyle endostomal. Outer integument ? cell layers thick. Inner integument ? cell layers thick. Hypostase present or absent. Parietal cell formed from archesporial cell. Megagametophyte monosporous, Polygonum type (in Groenlandia, Potamogeton, and Stuckenia) or disporous, Allium or Endymion type (in Zannichellia, Pseudalthenia and Althenia). Antipodal cells sometimes persistent and proliferating up to four or five cells. Suspensor prominent, vesicular. Endosperm development ab initio helobial. Endosperm haustoria? Embryogenesis caryophyllad.

Fruit Usually a drupe (in Groenlandia densa a berry, dehiscing by degradation of pericarp wall; in Althenia a follicle). Photosynthesizing.

Seeds Aril absent. Seed coat usually exotestal. Testa membranous, without phytomelan. Exotesta usually well developed. Tegmen unspecialized. Testa crushed in some species of Potamogeton and Zannichellia. Perisperm not developed. Endosperm absent. Embryo large, curved, spirally twisted (usually macropodous), well differentiated, without chlorophyll. Cotyledon one. Cotyledon hyperphyll elongate, assimilating. Hypocotyl large, rich in starch, with long internode. Coleoptile absent. Germination phanerocotylar.

Cytology n = 7, 12, 14–18, 26, 52, etc. – Polyploidy and aneuploidy frequently occurring. Chromosomes 0,5–2,3 μm long.

Phytochemistry Flavone aglucones, flavone-C-glycosides (in Zannichellia flavone-O-glycosides), and tannins (in Potamogeton) present. Flavonols and flavone sulphates present in Zannichellia. Anthocyanins, ellagic acid, proanthocyanidins, alkaloids, saponins, and cyanogenic compounds not found. Rhodoxanthin gives some species a red colour.

Distribution Temperate and subtropical regions on both hemispheres. Mainly in coastal marine environments.

Fossils Fossil fruits described as Limnocarpus from the Paleocene of western Europe have sometimes been assigned to Ruppiaceae.

Habit Bisexual, usually annual (rarely perennial) herbs. Aquatic in salt or brackish (rarely fresh) water. Submersed. Shoot apices usually not transformed into turions (present in Ruppia tuberosa).

Vegetative anatomy Mycorrhiza absent. Roots fibrous, non-septate. Phellogen absent. Secondary lateral growth absent. Vessels absent. Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Tanniniferous cells frequent. Calciumoxalate crystals and silica bodies absent.

Leaves Alternate (distichous), simple, entire, linear, often filiform, with ? ptyxis. Stipules absent; leaf sheath well developed, open, more or less auriculate, with basal membranous sheath-like ligule in transition zone to lamina; axillary intravaginal scales, squamulae intravaginales, numerous. Venation parallelodromous (leaf one-veined). Foliar vascular tissue reduced to a central strand and two indistinct strands along leaf margin. Stomata absent. Cuticular wax absent. Leaf margin subentire, at apex finely serrate.

Inflorescence Terminal, scapose one- or few-flowered head- or umbel-like spike, each one at an early stage surrounded by two bracts. Peduncle (scape) during fruit maturation much prolonged and approaching water surface or spiralling and forcing fruits downwards below water surface. Floral bracts absent.

Flowers Actinomorphic, small. Hypogyny. Tepals absent. Nectary absent. Disc absent.

Androecium Stamens two, median, free. Filaments absent. Anthers basifixed, non-versatile, tetrasporangiate, extrorse, longicidal (dehiscing by longitudinal slits)?; connective wide, with abaxial tepaloid appendage. Tapetum amoeboid-periplasmodial, with ab initio uninucleate cells. Staminodia absent.

Pollen grains Microsporogenesis successive. Pollen grains inaperturate, heteropolar, bilateral, elongate, often curved, floating on water surface, shed as monads, tricellular at dispersal. Exine semitectate (intectate at ends), with columellate infratectum, reticulate.

Gynoecium Carpels (two to) four (to 16), free. Ovary superior, unilocular (apocarpy), stipitate. Style absent. Stigmas peltate, lobate, non-papillate, Dry type. Pistillodia absent.

Ovules Placentation apical or lateral. Ovule one per carpel, campylotropous, pendulous, bitegmic, crassinucellar. Micropyle bistomal. Outer integument ? cell layers thick. Inner integument ? cell layers thick. Megagametophyte monosporous, Polygonum type. Endosperm development helobial. Endosperm haustoria? Embryogenesis caryophyllad.

Fruit A drupe, dehiscing by degradation of fleshy outer pericarp layers. Endocarp strongly sclerified, with two perforations in placental part, through which embryo germinates.

Seeds Aril absent. Testa two-layered. Exotesta? Endotesta? Exotegmic cells large with branched processes from walls, all crushed. Endotegmen? Perisperm not developed? Starch present. Endosperm absent. Embryo straight, curved or spirally twisted (macropodous), well differentiated, chlorophyll? Cotyledon one. Cotyledon hyperphyll elongate, assimilating. Hypocotyl large, with long internode. Coleoptile absent. Germination phanerocotylar?

Cytology n = 8, 10, 12, 20 – Karyotype bimodal, with nine small and one large chromosome. Chromosomes 0,7–4,4 μm long.

Phytochemistry Flavonols, flavone-O-glycosides, ellagic acid, and proanthocyanidins present. Sulphates? Alkaloids and saponins not found.

Rudolphi, Syst. Orb. Veg.: 28. 5-12 Jul 1830 [’Scheuchzerieae’], nom. cons.

Vegetative anatomy Phellogen absent. Outer cycle of vascular bundles connected by sclerenchyma and forming a continuous cylinder. Secondary lateral growth absent. Endodermis present in stem. Vessels present in roots. Vessel elements with scalariform perforation plates; lateral pits scalariform, simple pits. Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Tanniniferous cells present. Silica bodies absent. Calciumoxalate as druses or single prismatic crystals.

Leaves Alternate (distichous), simple, entire, linear, with ? ptyxis. Stipules absent; leaf sheath open, with two small auricles (biauriculate) and numerous filiform intravaginal scales, squamulae intravaginales. Venation parallelodromous. Stomata tetracytic. Cuticular wax absent. Air lacunae present. Mesophyll with cells containing calciumoxalate as druses or single prismatic crystals. Hypodermal rows of crystals surrounding vascular bundles. Tanniniferous cells abundant. Leaf margin entire. Pseudolamina with adaxial apical pore.

Flowers Actinomorphic, small. Hypogyny. Tepals 3+3, sepaloid to petaloid, free. Nectary absent. Disc absent.

Androecium Stamens 3+3. Filaments free from each other and from tepals. Anthers basifixed, non-versatile, tetrasporangiate, extrorse, longicidal (dehiscing by longitudinal slits). Tapetum amoeboid-periplasmodial, with ab initio uninucleate cells with degenerating walls. Staminodia absent.

Pollen grains Microsporogenesis successive? Pollen grains inaperturate, shed as dyads, tricellular at dispersal. Exine semitectate, with columellate infratectum, reticulate.

Gynoecium Pistil composed of usually three (rarely six) basally connate plicate antesepalous carpels, usually congenitally fused (carpel edges not entirely coherent). Ovary superior, usually trilocular (rarely sexalocular). Style absent. Stigma adaxially decurrent, papillate, Dry type. Pistillodium absent.

Ovules Placentation subbasal-axile. Ovules usually two (sometimes one) per carpel, anatropous, ascending, bitegmic, crassinucellar. Micropyle endostomal. Outer integument five or six cell layers thick. Inner integument approx. four cell layers thick. Parietal cell formed from archesporial cell. Megagametophyte monosporous, Polygonum type. Antipodal cells not formed; antipodal nuclei early degenerating. Endosperm development ab initio helobial. Endosperm haustorium micropylar? (absent?). Embryogenesis probably caryophyllad.

Fruit An assemblage of one- or two-seeded follicles (a schizocarp with three or rarely six mericarps).

Seeds Aril absent. Testa smooth. Tegmen? Perisperm not developed? Starch present. Endosperm absent. Embryo well differentiated, with chlorophyll. Cotyledon one, large, rounded, non-photosynthesizing. Cotyledon hyperphyll elongate to short (nutrient storing, with starch?). Hypocotyl internode absent. Coleoptile absent. Germination phanerocotylar.

Phytochemistry Tyrosine-derived cyanogenic glucosides (triglochinin) and cyanidin? present. Flavonoids, alkaloids and saponins not found. Unlignified cell walls lacking ferulate.

Distribution Temperate Eurasia, with their largest diversity in East Asia, southeastern United States, northwestern South America.

Vegetative anatomy Roots fibrous. Phellogen absent. Vessel elements with scalariform (to reticulate) perforation plates; lateral pits? Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Phloem with alternating sieve cells and fibres. Sieve tube plastids P2c_cp type, with starch, many cuneate protein crystals and a single polygonal protein crystal. Nodes? Parenchyma with a unique type of calciumoxalate druses. Envelopes of vascular bundles with prismatic crystals. Calciumoxalate raphides absent at least in Tofieldia.

Leaves Alternate (distichous), simple, entire, usually equitant (ensiform), isobifacial, with ? ptyxis. Stipules absent; leaf sheath well developed; ligule present in Pleea. Venation parallelodromous. Stomata anomocytic. Cuticular wax absent. Leaf margin entire.

Inflorescence Terminal, usually spike or raceme (flowers in Harperocallis rarely solitary). Floral bracts in Pleea spathe-like. A calyculus – consisting of one to three floral prophylls (bracteoles) – subtending each flower (absent in some species of Tofieldia).

Flowers Actinomorphic, small. Hypogyny. Tepals 3+3, petaloid, usually free (sometimes connate at base); median outer tepal in Tofieldia adaxial. Triradiate septal? nectaries usually present, on inner bases of connate carpellary stipes (perigonal nectaries sometimes present as well). Disc absent.

Androecium Stamens usually 3+3 (in Pleea 6+3, or rarely 6+4 or 6+6), usually free (sometimes connate at base), sometimes adnate to tepal bases. Anthers basifixed or subbasifixed, usually non-versatile, tetrasporangiate, introrse or latrorse, longicidal (dehiscing by longitudinal slits). Tapetum secretory, with binucleate cells. Staminodia absent.

Pollen grains Microsporogenesis simultaneous (Tofieldia). Pollen grains in Harperocallis at least sometimes monosulcate, in Pleea and Tofieldia usually disulcate (sometimes trichotomosulcate), shed as monads, bicellular at dispersal. Exine tectate or semitectate, with columellate infratectum, reticulate, microreticulate, rugulate, verrucate or gemmate (in species of Tofieldia).

Gynoecium Pistil composed of three at base (Pleea), half-way up (Tofieldia, Triantha?) or for most of their length (Harperocallis) connate carpels; carpel usually plicate, postgenitally fused with secretory canal; compitum formed by main parts of carpels. Ovary superior, usually trilocular (sometimes unilocular). Stylodia three, usually free (sometimes connate in lower part or only at base, in Harperocallis connate into a single simple style). Stigma capitate, type? Pistillodium absent.

Ovules Placentation usually axile (sometimes parietal, then ovary unilocular). Ovules five to numerous per carpel, anatropous to campylotropous, usually bitegmic? (in Tofieldia iridacea and Harperocallis duidae unitegmic), faintly crassinucellar. Micropyle ?-stomal. Outer integument ? cell layers thick. Inner integument ? cell layers thick. Obturator integumentary. Parietal tissue weakly developed. Nucellar cap sometimes present. Hypostase present. Megagametophyte in Tofieldia monosporous, modified Polygonum type (seven-celled and 11-nucleate), or disporous, Allium type or Veratrum lobelianum type (micropylar cell dividing prior to chalazal cell during second meiotic division of megagametophyte mother cell, leading to formation of ephemeral triad). Antipodal cells in Tofieldia binucleate, persistent, often proliferating. Long chalazal (funicular?) hooked extension present in Pleea and species of Tofieldia. Endosperm development helobial. Endosperm haustoria? Embryogenesis?

Fruit Usually a septicidal (Pleea, Harperocallis) or ventricidal (Tofieldia, Triantha) capsule or an assemblage of follicles (sometimes, e.g., in Isidrogalvia with persistent tepals).

Seeds Aril absent. Seeds in Pleea and Triantha with filiform terminal appendages at both ends, in Harperocallis with filiform chalazal appendage, decurrent along seed. Phlobaphene present at least in Tofieldia. Tegmen thin. Perisperm not developed. Endosperm copious. Embryo large, well differentiated, chlorophyll? Cotyledon one. Cotyledon hyperphyll? Hypocotyl internode? Coleoptile? Rhizoids in Harperocallis flava collar type. Radicula absent? Germination phanerocotylar.

Cytology x = (14) 15 (16) – Polyploidy rare. Chromosomes 0,9–2,5 µm long.

Phytochemistry Flavonols (kaempferol, quercetin), chelidonic acid, glycosides, and steroidal saponins present. Flavones not found.

Zosterales J. Presl in Nowočeská Bibl. [Wšobecný Rostl.] 7: 1667. 1846 [‘Zostereae’]; Zosteranae Doweld, Tent. Syst. Plant. Vasc.: lviii. 23 Dec 2001

Distribution Temperate marine coastal waters on both hemispheres; some species in tropical and subtropical marine coastal waters.

Fossils The Maastrichtian Archaeozostera from Japan may be assigned to Zosteraceae.

Habit Monoecious (Zostera, Nanozostera, Heterozostera) or dioecious (Phyllospadix), usually perennial (rarely annual) herbs. Marine (sometimes in brackish water). Submersed. Main stem with monopodial growth. Branches leaf-opposite.

Vegetative anatomy Mycorrhiza absent. Phellogen absent. Rhizome cortex usually with fibre strands (absent in Phyllospadix) and vascular bundles. Secondary lateral growth absent. Vessels absent. Imperforate tracheary xylem elements tracheids. Wood rays absent. Axial parenchyma? Sieve elements with thick nacreous cell walls (absent from roots). Sieve tube plastids P2c type, with cuneate protein crystalloid bodies, without starch or protein filaments. Nodes? Tanniniferous cells frequent. Crystals absent.

Leaves Alternate (distichous), simple, entire, linear, with convolute (supervolute) ptyxis? Stipules absent; leaf sheath well developed, open or closed, auriculate, with ligule in transition zone to lamina; axillary intravaginal filiform scales, squamulae intravaginales, two to four. Venation parallelodromous; primary veins connected? to transversal veins. Stomata absent. Cuticular wax absent. Mesophyll without calciumoxalate crystals. Leaf margin entire. Leaf with apical pore.

Inflorescence Axillary, flattened spike-like spadix with incurved margins and with flowers arranged into two dorsal-abaxial rows and enclosed by a sheathing spatha; inflorescence interpreted as a panicle consisting of one or more rhipidia, each of which with (one or) two to five spathae. In Zostera two male flowers alternating with one female flower along two inflorescence rows. Male or female flowers in Phyllospadix zig-zag arranged in spadix. Floral bracts and prophylls (bracteoles) absent. Inflorescence axis usually with marginal appendages, retinacula (absent from Zostera), each one surrounding and almost enclosing a single stamen.

Flowers Actinomorphic? (zygomorphic by reduction), small. Hypogyny? Tepals absent. Nectary absent. Disc absent.

Androecium Stamen one. Filament absent. Anther dorsifixed, non-versatile?, tetrasporangiate, extrorse, longicidal (dehiscing by longitudinal slits); connective with enlarged tepaloid appendage; stamen and tepaloid connective appendage supported by a common trace (vascular strand branch). Tapetum amoeboid-periplasmodial. Staminodia absent.

Pollen grains Microsporogenesis successive. Pollen grains inaperturate, filiform (up to 2 mm long), shed as monads, bicellular (Zostera, Nanozostera, Heterozostera) or tricellular (Phyllospadix) at dispersal. Exine absent. Pollen surface smooth.

Gynoecium Pistil composed of seemingly one carpel (in reality two carpels one of which reduced and sterile). Ovary superior?, unilocular (pseudomonomerous). Stylodium single, bilobate, short. Stigmas two, type? Pistillodium absent?

Ovules Placentation apical. Ovule one per ovary, orthotropous, pendulous, bitegmic, pseudocrassinucellar or tenuinucellar. Micropyle endostomal. Outer integument up to seven cell layers thick. Inner integument ? cell layers thick. Parietal cell not formed. Nucellar cap formed by periclinal cell divisions of megasporangial epidermis. Megagametophyte monosporous, Polygonum type. Antipodal cells not proliferating. Hypostase present. Endosperm development ab initio nuclear? Endosperm haustoria? Embryogenesis caryophyllad.

Fruit A usually nutlike fruit (in Phyllospadix with soft exocarp and hard fibrous endocarp).

Seeds Aril absent. Seed coat exotestal. Exotestal cells more or less anticlinally and periclinally elongate; remaining cells persistent, often more or less thickened. Tegmen degenerating. Perisperm not developed? Endosperm absent. Embryo somewhat curved (usually macropodous), well differentiated, chlorophyll? Cotyledon one. Starch? Cotyledon hyperphyll elongate, assimilating. Hypocotyl large, with long internode, basally as a large disc with rhizoids. Coleoptile absent. Radicula minute or absent. Germination phanerocotylar.

Cytology x = 6, 9, 10, 12 (Zostera), 18 (Heterozostera) – Chromosomes 0,9–1,6 μm long.

Phytochemistry Flavones, flavone sulphates, and sulphonated phenolic acids present. Flavonols, ellagic acid, and proanthocyanidins not found.

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NARTHECIIDAE S. W. Graham et W. S. Judd

ALISMATALES R. Br. ex Bercht. et J. Presl

ALISMATACEAE Vent.

APONOGETONACEAE Planch.

ARACEAE Juss.

BUTOMACEAE Mirb.

CYMODOCEACEAE Vines

HYDROCHARITACEAE Juss.

JUNCAGINACEAE A. Rich.

MAUNDIACEAE Nakai

POSIDONIACEAE Vines

POTAMOGETONACEAE Bercht. et J. Presl

RUPPIACEAE Horan.

SCHEUCHZERIACEAE F. Rudolphi

TOFIELDIACEAE Takht.

ZOSTERACEAE Dumort.