Herbs perennial, aquatic, without rhizomes; roots absent; air chambers conspicuous. Leaves arising from branched stems, sessile, whorled; stipules absent. Leaf blade undivided to finely dissected, margins serrulate, laticifers absent; 1st leaves of plumule simple or forked. Inflorescences axillary, solitary flowers. Flowers unisexual, staminate and pistillate on same plant, submersed, sessile or nearly so, subtended by involucre of 8-15 linear bracts; perianth absent; stamens 3-50; anthers nearly sessile, dehiscing by longitudinal slits, connective prolonged; pistil 1, simple; ovary 1-locular; placentation laminar; ovule 1; style elongate; stigma decurrent. Fruits achenes, indehiscent. Seed 1, aril absent; endosperm and perisperm absent; embryo well developed; cotyledons 2, fleshy.
Herbs perennial, submersed, hydrophilous, monoecious. Roots absent. Stems glabrous, branched, free or attached by slender shoots. Stipules absent. Leaves cauline, 3--11 in a whorl; petiole inconspicuous; leaf blade divided dichotomously into filiform segments; segments with 2 rows of denticles. Inflorescences reduced, solitary or with vestigial branches, 1-several at a node, extra-axillary, alternating with leaves, sessile or peduncles lengthening in fruit; involucre of 8--15 foliaceous bracts; bracts 1.5--2 mm, apex terminated by 2 denticles and a medial multicellular appendage. Flowers naked, subsessile. Staminate flower: stamens 3--50, spiral; filaments short; anthers 2-celled, dehiscing by longitudinal slits. Pistillate flower: pistil 1, simple; ovary 1-loculed, placentation laminar; ovule 1, pendulous; style persistent, short or elongate; stigma decurrent. Achene leathery, indehiscent, ellipsoid, smooth or tuberculate, basal spines 0--2, facial spines 0--2, marginal wing present or absent, marginal spines 1--8. Seed 1, unitegmic, endosperm and perisperm absent; cotyledons fleshy.
Seed pendulous; endosperm 0; embryo straight; cotyledons oblong, equal; radicle very short, the plumule already well developed and showing several leaves in the seed
Fruit a nut, ovoid or ellipsoid
Male flowers: stamens 10–22, crowded on a flat torus; anthers almost sessile, erect, linear-oblong, 2-celled, cells parallel, opening lengthwise; connective produced beyond the cells, thick and often coloured
Female flowers: staminodes 0; ovary sessile, ovoid, 1-celled; style continuous with the ovary
Flowers monoecious, solitary in the whorls, the males and females at separate nodes, sessile
Calyx thinly herbaceous, many-parted into narrow subvalvate segments often dentate or lacerate at the apex
Aquatic submerged herbs with leafy floating branches
Leaves verticillate, variously divided with thread-like or linear segments
Embryo straight, endosperm absent
Fruit a nut, ovoid or ellipsoid, often warty and basally-spined, style ± persistent, spinose
Female flowers sessile or shortly pedicellate; staminodes absent; ovary superior, sessile, ovoid, tapering into a long style; ovule 1, pendulous
Male flowers subsessile; stamens up to c. 30 in several whorls on a domed torus around the pistillode; filaments short or absent; anthers oblong, extrorse, 2-locular, dehiscing longitudinally, connective produced apically into 2 spines and a central projection as in perianth lobes, immature anthers resembling perianth lobes, margins 1–3 spined; mature anthers detach and float to the water-surface where they dehisce and shed pollen on to plants below
Flowers axillary, 1-several per node, male and female flowers at different nodes, ± sessile; perianth lobes 6–13, united at the base, strap-shaped or obovate, margin often with a single lateral hyaline spine or ± lacerate, apex as for leaf apex
Leaves in whorls, filiform, once or more dichotomously branched, margins ± spinose-dentate; apical segments truncate, 2-spined at the apex with a reddish glandular projection between the spines (basal segments sometimes parasitised, becoming swollen and sac-like)
Submerged aquatic, branching, usually rootless herbs, perennating by buds, monoecious
Aquatic herbs, monoecious, perennating by buds, usually free-floating
Leaves in whorls of (6–)8–11, filiform, dichotomously branched, often with few–many spine-tipped teeth on margins especially of distal segments; terminal segments truncate, 2-spined and with a central reddish terete soon deciduous projection ± 0.2 mm. long
Perianth of 6–13 strap-shaped or obovate lobes united at base and some united in pairs to over half their length, often with a single hyaline spine on each margin, truncate with 2 spines and a central projection as in leaves
Flowers axillary, 1-several per node, ? and ? at different nodes
Female flowers sessile or shortly pedicellate, without staminodes; ovary solitary, superior, sessile, tapering into long style; ovule 1, pendulous
Male flowers subsessile, with numerous stamens in several whorls on domed torus around pistillode; filaments very short or absent; anthers oblong, extrorse; thecae 2, parallel, dehiscing longitudinally; connective produced apically into 2 spines and a central projection as in perianth-lobes, often with 1–3 spines on margins; immature anthers much flattened, resembling perianth-lobes, later swollen, oblong, reddish projection detaching, tissues becoming gas-filled and bearing detached anther to water-surface where it becomes horizontal, dehisces and sheds pollen on to plants below
Fruit a hard nut, ovoid or ellipsoid, slightly laterally flattened, wingless and rimless, or more markedly flattened and then often with marginal longitudinal ‘rim’ or entire to dentate or spinulose wing; style ± persistent and spinose; base often with a pair of prominent spines; rest of surface often gland-dotted, spiny or warty; embryo straight; endosperm absent
Herbes'monoïques submergées, flottantes, sans racines.'Feuilles'verticillées par 6-10, linéaires, 2 à 4 fois dichotomiques, à divisions étalées en éventail et ± échinulées.'Fleurs'petites, ♂♀, axillaires, solitaires et subsessiles; périgone de 6-10 segments linéaires, aigus, ± denticulés; étamines nombreuses, dressées, dépassant à peine le périgone; anthères subsessiles à connectif ± denticulé et glanduleux, dépassant les loges; ovaire 1-carpellaire; style long et aigu; ovule unique, orthotrope.'Akènes ellipsoïdes, comprimés, biconvexes, 5-6 fois plus longs que le périgone persistant, ± glanduleux, inermes ou présentant des appendices épineux variables avec les espèces et les variétés.\n\t\t\tFamille aberrante comprenant 1 genre et 3 espèces cosmopolites, très voisines et mal définies (réunies en une seule avec 7 variétés par Schumann, Mart., Fl. Bras., III, 3, p. 747, t. 125, 1894); 1 ou 2 (? au Congo belge.
Chase, M. W. et al. 1993. Phylogenetics of seed plants: An analysis of nucleotide sequences from the plastid gene rbcL. Ann. Missouri Bot. Gard. 80: 528-580. Dilcher, D. L. 1990. The occurrence of fruits with affinities to Ceratophyllaceae in lower and mid-Cretaceous sediments. [Abstract.] Amer. J. Bot. 76: 162. Les, D. H. 1988. The origin and affinities of the Ceratophyllaceae. Taxon 37: 326-345. Les, D. H. 1993. Ceratophyllaceae. In: K. Kubitzki et al., eds. 1990+. The Families and Genera of Vascular Plants. 2+ vols. Berlin etc. Vol. 2, pp. 246-250. Les, D. H., D. K. Garvin, and C. F. Wimpee. 1991. Molecular evolutionary history of ancient aquatic angiosperms. Proc. Natl. Acad. Sci. U.S.A. 88: 10119-10123. Qiu Y. L., M. W. Chase, D. H. Les, and C. R. Parks. 1993. Molecular phylogenetics of the Magnoliidae: Cladistic analyses of nucleotide sequences of the plastid gene rbcL. Ann. Missouri Bot. Gard. 80: 587-606. Wood, C. E. Jr. 1959. The genera of the Nymphaeaceae and Ceratophyllaceae in the southeastern United States. J. Arnold Arbor. 40: 94-112.