SUPERTRICOLPATAE


[Ceratophyllum+Tricolpatae]


CERATOPHYLLACEAE Gray

Gray, Nat. Arr. Brit. Pl. 2: 395, 554. 22 Jan 1822 [’Ceratophyllae’], nom. cons.

Ceratophyllales Link, Handbuch 2: 406. 4-11 Jul 1829 [‘Ceratophylleae’]; Ceratophyllanae Takht. ex Reveal et Doweld in Novon 9: 549. 30 Dec 1999; Ceratophyllidae Doweld, Tent. Syst. Plant. Vasc.: xxv. 23 Dec 2001

Genera/species 1/2–6

Distribution Cosmopolitan except polar areas.

Fossils Fossil fruits, Donlesia dakotensis, from the latest Albian to the earliest Cenomanian (mid-Cretaceous) may be closely allied to Ceratophyllaceae, although it had basal placentation. Ceratostratiotes cretaceus, a fruit impression, was described from the Late Cretaceous of Israel, although its affinity to Ceratophyllaceae may be questioned. Ceratophyllum is frequent in layers from the Early to Late Cenozoic in the Northern Hemisphere. Fossil pollen grains are unknown.

Habit Monoecious, perennial herbs. Aquatic, with submersed stems and leaves, sometimes anchored in the sediment through rhizoid branches. Branches extra-axillary, alternating with leaves. Roots absent.

Vegetative anatomy Mycorrhiza absent. Phellogen absent. Aerenchyma schizogenous, as cylinder of air canals outside pericycle. Cambium and secondary lateral growth absent. Stem vascular tissue protostele (xylem with or without central air lacuna, with or without chloroplasts). Vessels absent. Imperforate tracheary xylem elements tracheids modified into unlignified elongate cells, starchy and tanniniferous. Wood rays absent. Axial parenchyma absent. Sieve tube plastids Ss type, with approx. ten starch grains. Nodes? Idioblasts absent. Crystals?

Trichomes Hairs usually absent (sometimes present, unicellular).

Leaves Usually verticillate (first leaves opposite), usually two to several times dichotomously divided with filiform lobes, with ? ptyxis. Stipules and leaf sheath absent. Petiole vascular bundle transection? Stomata absent. Cuticular waxes absent. Secretory glands abundant. Leaflet margins spinulose. Leaf tip with multicellular mucilaginous appendage.

Inflorescence Flowers extra-axillary, alternating with leaves, usually solitary (rarely several together). Floral prophylls (bracteoles) possibly absent.

Flowers Actinomorphic, small, sessile. Hypogyny? Tepals probably absent; replaced by whorl of six to 15 bracts (tepals?) connate at base and non-vascularized. Nectary absent. Disc absent.

Androecium Stamens three to 46, spiral. Filaments very short, flattened, free. Anthers basifixed, non-versatile, tetrasporangiate, extrorse-latrorse, longicidal (dehiscing by longitudinal slits) or irregularly dehiscent; connective flattened, thick, spur-like, prolonged, with spinulose-dentate edges. Tapetum secretory or amoeboid-periplasmodial, with uninucleate cells. Staminodia absent.

Pollen grains Microsporogenesis successive (in, e.g., Ceratophyllum demersum and C. submersum) or simultaneous (in, e.g., C. pentacanthum). Pollen grains inaperturate (to indistinctly monosulcate?), shed as monads, bicellular at dispersal. Exine highly reduced. Pollen grains with numerous starch grains. Pollen tube very long, spirally twisted, sometimes branched.

Gynoecium Pistil composed of usually a single carpel (rarely two free carpels, apocarpy); carpel ascidiate, postgenitally occluded by secretion, bilaterally symmetric. Ovary superior?, unilocular. Style short to relatively long, subulate, with stylar canal and usually entire (sometimes slightly bifid) apex. Stigma minute, as a pocket at orifice of stylar canal, without viscid secretions, Dry type. Pistillodium absent.

Ovules Placentation apical-ventral (or laminar-dorsal). Ovule one per ovary, almost orthotropous, pendulous, unitegmic, crassinucellar. Funicle without vascular strand. Integument four cell layers thick at base, two or three cell layers thick in middle, one cell layer thick at apex. Nucellar cap present. Hypostase tanniniferous. Megagametophyte monosporous, Polygonum type. Antipodal cells persistent. Endosperm development cellular. Endosperm haustorium chalazal (four large lower cells of endosperm haustorial). Embryogenesis asterad.

Fruit An achene, usually with warts, tubercles, spinules or wings, and with persistent style.

Seeds Aril absent. Seed coat thin and transparent, formed by outer epidermis of megasporangium. Testa absent or almost absent. Perisperm not developed. Endosperm thin, chalazal, mucilaginous, or absent. Suspensor absent. Embryo large, straight, with chlorophyll. Cotyledons two, thick, fleshy. Plumule large, green, consisting of eight to ten whorls of leaves, and a few lateral buds. Radicula minute, rudimentary and undifferentiated, ephemeral. Germination phanerocotylar.

Cytology n = 12, (19, 20, 24) 36 – Polyploidy occurring.

DNA

Phytochemistry Flavonols, flavone-O-glycosides, glycoflavones, anthocyanins, cyanidin, proanthocyanidins (prodelphinidins), and phenols present. Ellagic acids, alkaloids, and ethereal oils not found.

Use Aquarium plants, medicinal plants.

Systematics Ceratophyllum (2–6; nearly cosmopolitan).

Ceratophyllum has often been recovered as sister to either Tricolpatae or Liliidae (see, e.g. Barniske & al. 2012). Absence of ethereal oils may be a synapomorphy uniting Ceratophyllum with the tricolpates. However, in a four-gene study of mitochondrial DNA, Ceratophyllum was identified as sister to Chloranthaceae (Qiu & al. 2010). Likewise, Moore & al. (2011) found Ceratophyllum to be sister to Chloranthaceae based on an analysis of the plastid inverted repeat. The clade [Chloranthaceae+Ceratophyllum] was sister to the tricolpates. Barniske & al. (2012) recovered Ceratophyllum as sister to either Acorus (maximum parsimony strict consensus using substitutions and indels of all plastid genome regions) or all eudicots (maximum likelihood based on combined analyses of a number of intergenic spacers; then Acorus was sister to Chloranthus).

Species delimitations are notoriously problematical in Ceratophyllum.


Literature

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