DIDYMELIDAE


[Didymelales+Gunneridae]


DIDYMELALES Takht.

Takhtajan, Sist. Filog. Cvetk. Rast. [Syst. Phylog. Magnoliophyt.]: 118. 4 Feb 1967

Fossils The Late Albian to Early Cenomanian Spanomera from Maryland is represented by monoecious decussate inflorescences with units bearing a terminal female flower and a pair of lateral male flowers. The pollen grains are tricolpate, the two carpels basally slightly connate and the fruits follicular. Lusistemon striatus is male flowers with up to six antetepalous stamens from the Late Aptian to the Early Albian of Portugal. The pollen grains are tricolpate with a striate exine, and the fruits – developed from two connate carpels – have been described as Lusicarpus planatus. Aguacarpus hirsutus and Valecarpus pedicellatus comprise two tricarpellate syncarpous gynoecia with reflexed styles from the Late Aptian to the Early Albian of Portugal.

Habit Usually monoecious (rarely dioecious, polygamodioecious or bisexual), evergreen trees or shrubs (sometimes perennial herbs).

Vegetative anatomy Phellogen ab initio subepidermal or pericyclic. Vessel elements with scalariform perforation plates; lateral pits usually opposite or alternate (rarely intermediary between scalariform and opposite), bordered pits. Imperforate tracheary xylem elements usually vessel-like tracheids (rarely fibre tracheids) with usually bordered (sometimes simple) pits, non-septate (also vasicentric tracheids). Wood rays uniseriate or multiseriate, homocellular or heterocellular. Axial parenchyma usually apotracheal diffuse or diffuse-in-aggregates, or paratracheal scanty (sometimes unilateral; occasionally absent). Compression wood present. Parenchyma often with secretory cells and sclereids. Sieve tube plastids Pc or Pcs type, with a central globular protein crystal. Nodes 1:1, unilocular with one leaf trace. Druses sometimes present. Chains of small irregularly thickened sclereids with calciumoxalate crystals, surrounding a larger fibre, sometimes present.

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

Leaves Alternate (spiral) or opposite, simple, entire, usually coriaceous, with ? ptyxis. Stipules and leaf sheath absent. Petiole vascular bundle transection arcuate. Venation usually pinnate, usually brochidodromous (rarely craspedodromous, eucamptodromous or palmate). Stomata usually laterocytic (sometimes cyclocytic or anomocytic). Cuticular wax crystalloids as curved rods or irregular platelets. Mesophyll often with sclerenchymatous idioblasts. Lamina usually with secretory canals. Idioblasts with ethereal oils absent. Calciumoxalate as druses or single prismatic crystals. Leaf margin usually entire (rarely serrate, with chloranthoid teeth). Peltate hairs sometimes present.

Inflorescence Usually terminal or axillary (or supra-axillary) racemes, spikes, heads or panicles (female flowers sometimes solitary, axillary).

Flowers Actinomorphic, small. Hypogyny. Tepals in male flowers (two to) four (or five), sepaloid or bracteate, with decussate or imbricate aestivation, connate at base (sometimes absent); tepals in female flowers (one to) four to six (rarely up to c. 20 or absent), some of them usually spiral. Nectaries often present between stylodia (sometimes absent). Disc absent.

Androecium Stamens (two or) four (or six; rarely up to c. 45), antetepalous (when six stamens, then two pairs opposite inner tepals). Filaments usually free from each other (sometimes connate at base) and from tepals (sometimes absent). Anthers basifixed or dorsifixed, non-versatile, tetrasporangiate, usually introrse (sometimes extrorse), longicidal (dehiscing by longitudinal slits). Tapetum secretory. Female flowers often with staminodia?

Pollen grains Microsporogenesis simultaneous. Pollen grains 3–7-zonocolporate, 5–12-pantocolporate (with two or more ora per colpus), 5–12-pantocolpate or 12–40-pantoporate (sometimes colpodiorate), with circular ectoapertures, shed as monads, bicellular at dispersal. Exine semitectate, with columellate infratectum, reticulate, often with supratectal spinules or pilate-verrucate elements (tectum rarely crotonoid, with pores and lumina surrounded by upraised structures consisting of discoid or triangular elements).

Gynoecium Pistil composed of one to four almost free carpels; carpel plicate, postgenitally completely fused, without canal. Ovary superior, uni-, bi- or trilocular (sometimes quadri- or sexalocular due to secondary septum). Stylodium one or absent, or stylodia two to four, marginal, usually free (rarely connate at base), with two crests. Stigmas usually decurrent (stylodia often stigmatic their entire length; rarely truncate), often with a median furrow (rarely somewhat connate at base), papillate, Dry or Wet type. Male flowers usually with pistillodium.

Ovules Placentation axile to apical. Ovules (one or) two per carpel, anatropous, hemianatropous or campylotropous, pendulous, apotropous or epitropous, bitegmic, crassinucellar. Micropyle usually endostomal (sometimes bistomal or exostomal). Placental obturator usually present. Nucellar cap usually well developed. Megagametophyte monosporous, Polygonum type. Synergids usually with a filiform apparatus. Antipodal cells sometimes proliferating. Endosperm development usually cellular (rarely nuclear). Endosperm haustoria? Embryogenesis onagrad.

Fruit Usually a loculicidal capsule with persistent style (sometimes a berry or a drupe).

Seeds Aril rudimentary or absent. Seeds often with caruncle formed from outer integument. Seed coat exotestal-mesotestal. Testa sometimes multiplicative. Exotesta palisade, with lignified cell walls. Mesotesta sometimes sclerotic. Endotesta often palisade. Tegmen unspecialized? Perisperm usually not developed. Endosperm copious, oily. Embryo short to long, usually straight (rarely curved), well differentated, without chlorophyll. Cotyledons two. Germination phanerocotylar.

Cytology n = 10, 12–14, 24, 27.

DNA Mitochondrial genes rps2 and rps11 absent (lost). Nuclear gene paleoAP3?

Phytochemistry Flavonols (kaempferol, quercetin), iridoids, proanthocyanidins, steroidal pregnane pseudoalkaloids (aminopregnanes, formed from triterpenoids), dhurrin (a cyanogenic glycoside), pinitol, simmondsin-like compounds, and arbutin present. Ellagic acid, tannins, benzylisoquinoline alkaloids, and saponins not found.

Systematics Buxaceae are sister to Didymeles (Didymelaceae).

BUXACEAE Dumort.

( Back to Didymelales )

Dumortier, Comment. Bot.: 54. Nov-Dec 1822 [‘Buxacia’, ‘Buxaceae’], nom. cons.

Pachysandraceae J. Agardh, Theoria Syst. Plant.: 358. Apr-Sep 1858 [‘Pachysandreae’]; Stylocerataceae (Pax) Takht. ex Reveal et Hoogland in Bull. Mus. Natl. Hist. Nat., sér. 4, sect. B, Adansonia, 12: 206. 24 Nov 1990; Buxales Takht. ex Reveal in Novon 2: 238. 13 Oct 1992; Buxanae (Müll. Arg.) Takht. ex Reveal et Doweld in Novon 9: 549. 30 Dec 1999; Haptanthaceae C. Nelson in Ceiba 42: 33. Mai 2001

Genera/species 5/90–120

Distribution Tropical and southern Africa, Madagascar, Socotra, northeastern Africa, northern Macaronesia, western and central Mediterranean, eastern Turkey, Caucasus and northern Iran, Afghanistan, Himalaya, southern India, Sri Lanka, East Asia to the Korean Peninsula and Japan, Southeast Asia, West and Central Malesia, southern North America, Central America, northwestern South America (the Andes).

Fossils Polyporate pollen grains similar to those in some extant Buxaceae have been found in Campanian to Maastrichtian and Cenozoic layers in Europe, Siberia and North America, and described as Erdtmanipollis. Paleocene and younger pollen grains assigned to Buxapollis and similar to Buxus are known from several sites in the Northern Hemisphere.

Habit Usually monoecious (rarely dioecious, polygamodioecious or bisexual), evergreen trees or shrubs; Pachysandra consists of perennial herbs with a rhizome.

Vegetative anatomy Phellogen ab initio subepidermal or pericyclic. Primary cortex with long fibres and large stone cells. Vessel elements with scalariform perforation plates; lateral pits usually opposite or alternate (in, e.g., Styloceras intermediary between scalariform and opposite), bordered pits. Imperforate tracheary xylem elements usually vessel-like tracheids (in Styloceras fibre tracheids) with usually bordered pits (sometimes simple pits), non-septate (also vasicentric tracheids). Wood rays uniseriate or multiseriate, homocellular or heterocellular. Axial parenchyma usually apotracheal diffuse or diffuse-in-aggregates, or paratracheal scanty (sometimes unilateral; occasionally absent). Parenchyma with secretory cells, single or in branched rows. Sieve tube plastids Pc or Pcs type, with a central globular protein crystal, with or without starch grains. Nodes 1:1, unilocular with one leaf trace, or 3:3, trilocular with one trace (in Sarcococca 1:3, unilocular with three traces). Heartwood sometimes with resinous substances. Chains of small irregularly thickened sclereids with calciumoxalate crystals, surrounding a larger fibre, present in Sarcococca.

Trichomes Hairs usually unicellular (sometimes multicellular, uniseriate), or absent.

Leaves Alternate (spiral; Pachysandra, Sarcococca, Styloceras) or opposite (Buxus, Haptanthus), simple, entire, usually coriaceous, with curved or flat ptyxis. Stipules and leaf sheath absent. Petiole vascular bundle transection arcuate, three bundles present in upper part of petiole. Venation usually pinnate, usually brochidodromous (in Pachysandra craspedodromous, in Styloceras eucamptodromous; rarely almost palmate). Stomata usually laterocytic (sometimes cyclocytic or anomocytic). Cuticular wax crystalloids as twisted rodlets or irregular platelets or as transitional types between twisted rodlets and tubuli, chemically characterized by presence of β-diketones. Lamina with secretory cells and secretory canals. Idioblasts with ethereal oils absent. Calciumoxalate as druses or single prismatic crystals. Lamina usually entire (in Pachysandra serrate, with chloranthoid teeth).

Inflorescence Usually terminal or axillary raceme or botryoid, spike- or head-like (female flowers sometimes solitary, axillary); in Buxus terminal flower of cyme female and lateral flowers male; in Pachysandra lowermost lateral flower of cyme female and remaining flowers male; in Haptanthus terminal stipitate female flower subtended by raceme-like cymose male partial inflorescence. Female flowers in Buxus subtended by bract-like paired scales.

Flowers Actinomorphic, small. Hypogyny. Tepals in male flowers (two to) four (or five), sepaloid or bracteate (in Haptanthus four, very small, or absent), decussate, with imbricate aestivation, connate at base (absent in Styloceras); tepals in female flowers usually four to six (rarely up to c. 20; in Haptanthus very small or absent), spiral (at least some), free? Nectaries in Buxus inserted between stylodia (not in Pachysandra, Sarcococca and Styloceras). Disc absent.

Androecium Stamens usually four (sometimes three or six; in Styloceras six to c. 45; in Haptanthus two), antetepalous (when six stamens, then two pairs opposite inner tepals); stamens in Pachysandra, Sarcococca and Styloceras showy. Filaments often wide, strongly exserted, free from each other and from tepals (in Haptanthus adnate to an elliptic structure [filament?] with an arcuate vascular bundle), in Buxus very short or absent. Anthers basifixed or dorsifixed, non-versatile, tetrasporangiate, introrse, longicidal (dehiscing by longitudinal slits); endothecium in Haptanthus significantly developed, massive. Tapetum secretory, with binucleate cells. Staminodia absent.

Pollen grains Microsporogenesis simultaneous. Pollen grains 3–7-zonocolporate, 5–12-pantocolporate (with two or more ora in each colpus), 5–12-pantocolpate or 12–40-pantoporate (in Haptanthus tricolp[oroid]ate), shed as monads, bicellular at dispersal. Exine semitectate, with columellate infratectum, reticulate, often with spinules or supratectal pilate-verrucate elements (Sarcococca with crotonoid tectum, pores and lumina surrounded by upraised structures consisting of discoid and triangular elements).

Gynoecium Pistil in Buxus and Haptanthus composed of usually three (sometimes four), in Pachysandra, Sarcococca and Styloceras usually two, almost free carpels; carpel plicate, postgenitally completely fused, without canal. Ovary superior, usually bi- or trilocular (in Pachysandra and Styloceras quadri- or sexalocular due to secondary septum; in Haptanthus unilocular). Styles (stylodia) usually three (sometimes two or four; in Haptanthus absent), marginal, usually free (rarely connate at base), often persistent. Stigmas bilobate, decurrent, wide, often with a median furrow (rarely somewhat connate at base; in Haptanthus trilobate with recurved lobes, stigmatic their entire length), papillate, Dry or slightly Wet type. Male flowers usually with pistillodium (absent in, e.g., Haptanthus).

Ovules Placentation usually axile to apical (parietal in Haptanthus). Ovules usually two (in Haptanthus eight to 15) per carpel, anatropous or campylotropous, pendulous, apotropous, bitegmic, crassinucellar. Micropyle in Buxus endostomal, in Pachysandra, Sarcococca and Styloceras bistomal. Outer integument two to ten cell layers thick. Inner integument two or three cell layers thick. Obturator, formed from placenta, usually present (absent in Styloceras?). Parietal tissue four to more than 15 cell layers thick. Nucellar cap present, often weakly developed. Megagametophyte monosporous, Polygonum type. Synergids with a filiform apparatus. Antipodal cells sometimes proliferating. Endosperm development usually ab initio cellular (in Sarcococca nuclear). Endosperm haustoria? Embryogenesis onagrad.

Fruit A loculicidal capsule (Buxus, Pachysandra), with persistent style, or baccate to drupaceous (Sarcococca, Styloceras); in Haptanthus unknown.

Seeds Seeds often with caruncle (in Buxus rudimentary), formed from outer integument. Seed coat exotestal-mesotestal. Testa in Pachysandra and Sarcococca multiplicative. Exotestal cells with lignified walls, palisade. Mesotesta sometimes sclerotized. Endotesta often palisade. Tegmen unspecialized? Hypodermal cell walls often lignified. Perisperm usually not developed (present in Sarcococca). Endosperm copious, oily. Embryo short to elongate, usually straight (rarely curved), well differentated, without chlorophyll. Cotyledons two, thin, flattened. Germination phanerocotylar.

Cytology n = 10, 12–14, 24, 27 – Agamospermy occurring in some species of Sarcococca.

DNA Mitochondrial genes rps2 and rps11 absent (lost). Nuclear gene paleoAP3?

Phytochemistry Flavonols (kaempferol, quercetin), steroidal pregnane alkaloids (aminopregnanes), triterpene alkaloids (e.g. cycloprotobuxine-C and buxamine-G), proanthocyanidins, dhurrin (a cyanogenic glycoside), arbutin, pinitol, and simmondsin-like compounds present. Iridoids? Ellagic acid, tannins, benzylisoquinoline alkaloids, and saponins not found. Raffinose and stachyose often present in phloem exudate. Nickel accumulated in some species of Buxus.

Use Ornamental plants (Buxus sempervirens, Pachysandra terminalis etc.), timber, carpentry, engravings (Buxus).

Systematics Buxaceae are sister to Didymeles (Didymelaceae).

Buxus is probably sister to the remaining Buxaceae.

Buxeae Dumort., Anal. Fam. Plant.: 45. 1829 [‘Buxineae’]

1/70–100. Buxus (70–100; western and southern Europe, northern Africa and southwards to South Africa, Madagascar, southwestern, southern and eastern Asia, Central America and the West Indies, especially Cuba). – Cortical vascular bundles sometimes present. Female inflorescences with opposite basal bracteoid scale-like leaves. Hypogyny. Nectaries usually present between stylodia (sometimes absent). Pollen grains tri- to polycolpate (colpus with two to four endoapertures) or polyporate. Carpels three, median carpel adaxial. Micropyle endostomal. Outer integument five to ten cell layers thick. Capsule loculicidal, explosively dehiscent. Seeds with rudimentary caruncle. Embryo curved. Radicula elongated. n = 14, 20. – The pollen grains in Buxus have often several ora per colpus and hence are similar to those in Didymeles (Didymelaceae).

Stylocerateae Pax in Engler et Prantl, Nat. Pflanzenfam. III, 5: 132, 134. Jun 1892 [‘Stylocereae’]

4/22. Haptanthus (1; H. hazlettii; Matarras in Honduras); Sarcococca (11; tropical and subtropical Asia from Afghanistan to China, Southeast Asia, Malesia including the Philippines, Guatemala?), Pachysandra (5; India, Nepal, Burma, China, Japan, Taiwan, southeastern United States), Styloceras (5; the Andes in South America). – East Asia southwards to West Malesia, eastern North America, northern South America. Fibres in Haptanthus storied. Nodes 1:3 (Sarcococca). Chains of small irregularly thickened sclereids, containing calciumoxalate crystals, surrounding a larger fibre. Leaves usually spiral. Female flowers with numerous spiral bracts. Floral prophylls (bracteoles) absent in Haptanthus. Male flowers in Styloceras and Haptanthus without perianth. Nectary absent. Stamens usually four (in Styloceras six to c. 45; in Haptanthus two, with wide filaments and anthers attached their entire length). Pollen grains pantoporate, with crotonoid exine surface elements. Carpels usually two (sometimes with divided loculi; in Haptanthus three, stipitate). Male flowers usually with pistillodium (pistillodium absent in Haptanthus). Placentation in Haptanthus parietal. Ovules eight to 15 per carpel. Micropyle bistomal. Outer integument usually two or three cell layers thick. Endosperm development in Sarcococca nuclear. Testa often multiplicative. Endotegmic cell walls at least in Sarcococca lignified. Perisperm present in Sarcococca. Embryo with short radicula. n = 12–14. – Haptanthus may be sister to the remaining three genera in Stylocerateae, according to maximum parsimony analyses (Shipunov & Shipunova 2011).

Cladogram of Buxaceae based on DNA sequence data (Shipunov & Shipunova 2011). The position of Haptanthus is somewhat uncertain, since it may be sister to Buxus, according to some gene data.

DIDYMELACEAE Leandri

( Back to Didymelales )

Leandri in Ann. Sci. Nat., Bot., sér. 10, 19: 316. Mai 1937

Genera/species 1/2

Distribution Eastern and northern Madagascar, the Comoro Islands.

Fossils Uncertain. Pollen grains which have been found in Palaeogene layers in the Ninetyeast Ridge in the Indian Ocean, in Australia and in New Zealand have been described as Schizocolpus marlinensis and may be assigned to Didymelaceae.

Habit Dioecious, evergreen trees.

Vegatative anatomy Phellogen? Cork tissue late and/or weakly developed. Medulla wide, chambered. Non-xylem tissues in bark, stem and leaves with numerous corse, thick fibres. Vessel elements with scalariform perforation plates; lateral pits opposite or alternate, bordered pits? Imperforate tracheary xylem elements tracheids with small bordered pits, non-septate? Pericyclic fibres absent. Wood rays multiseriate?, heterocellular, ten to c. 30 cells tall, with wings of erect cells. Axial parenchyma absent, replaced by lignified cells. Sieve tube plastids ? type. Nodes? Secretory canals absent. Pericyclic and cortical sclereids present. Druses present.

Trichomes Hairs small, peltate (on leaves).

Leaves Alternate (spiral), simple, entire, often coriaceous, with ? ptyxis. Stipules and leaf sheath absent. Petiole vascular bundle transection arcuate with one central and two inverted lateral vascular bundles. Venation pinnate, brochidodromous. Stomata cyclocytic. Cuticular waxes? Mesophyll with sclerenchymatous idioblasts. Calciumoxalate druses present. Leaf margin entire.

Inflorescence Axillary (or supra-axillary), raceme-like (with female flowers solitary or three together) or short panicle (reduced thyrso-paniculate?; with male flowers).

Flowers Actinomorphic, small. Hypogyny. Male flowers without tepals, often with one or two scales (floral prophylls?). Female flowers (in axil of bract) with one to three scale-like tepals (floral prophylls and bract?) or without tepals. Nectary absent. Disc absent.

Androecium Stamens two. Filaments short, connate at base. Anthers basifixed to somewhat dorsifixed, non-versatile, tetrasporangiate, extrorse, longicidal (dehiscing with longitudinal slits). Tapetum? Staminodia absent.

Pollen grains Microsporogenesis? Pollen grains tricolpodiorate (with two ora per colpus) with linear operculum in colpus, shed as monads, ?-cellular at dispersal. Exine semitectate, with columellate simplibaculate infratectum, reticulate.

Gynoecium Pistil composed of one carpel with adaxial suture; carpel plicate? Ovary superior, unilocular (monocarpellate). Scale-like structure present between bract and ovule. Stylodium very short or absent. Stigma truncate or obliquely decurrent, bifid, papillate, type? Pistillodium absent.

Ovules Placentation apical or subapical. Ovule usually one (rarely two) per carpel, hemianatropous, pendulous, epitropous, bitegmic, crassinucellar. Micropyle exostomal. Integuments prolonged to an elongate annular collar into stylar canal. Outer integument ? cell layers thick, fimbriate at apex. Inner integument ? cell layers thick. Chalaza conically prolonged. Megagametophyte monosporous, Polygonum type? Endosperm development cellular? Endosperm haustoria? Embryogenesis?

Fruit A one-seeded drupe with lateral furrow and persistent stigma.

Seeds Aril rudimentary or absent. Seed coat testal? Testal cell walls thickened (lignified?). Tegmen? Perisperm not developed? Endosperm absent. Embryo large, straight, well differentiated, chlorophyll? Cotyledons two, thick. Germination?

Cytology n = ?

DNA Mitochondrial genes rps2 and rps11 absent? Nuclear gene paleoAP3?

Phytochemistry: Insufficiently known. Steroid pregnane pseudoalkaloids (aminopregnanes) present. Iridoids? Aluminium accumulated.

Use Unknown.

Systematics Didymeles (2; D. integrifolia: eastern coast of Madagascar, Moheli in the Comoro Islands; D. perrieri: Tsaratanana, Montagne d’Ambre and Andohahela in Madagascar).

Didymeles is sister to Buxaceae.


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