Habit and leaf form. Aquatic herbs; laticiferous. Hydrophytic; free floating, or rooted. Leaves of rooted plants submerged and emergent. Heterophyllous (the submerged leaves linear, the emergent leaves petiolate with lanceolate or ovate lamina), or not heterophyllous. Leaves alternate; spiral to distichous (spirodistichous); at least when emergent, petiolate; sheathing. Leaf sheaths with free margins. Leaves simple; epulvinate. Lamina entire; linear, or lanceolate, or oblong, or obovate; parallel-veined, or pinnately veined (parallel-pinnate in the mature blade); cross-venulate. Axillary scales present. Lamina margins entire.
General anatomy. Plants without laticifers.
Leaf anatomy. Stomata present; paracytic.
Lamina with secretory cavities. Secretory cavities containing latex. The mesophyll not containing mucilage cells; without calcium oxalate crystals. Minor leaf veins without phloem transfer cells (Hydrocleys, Limnocharis). Vessels absent.
Stem anatomy. Secretory cavities present; with latex. Secondary thickening absent. Xylem without vessels. Sieve-tube plastids P-type; type II.
Root anatomy. Root xylem with vessels; vessel end-walls scalariform and simple.
Reproductive type, pollination. Plants hermaphrodite. Floral nectaries present. Nectar secretion from the gynoecium (basally from the bases of the sides of the carpels).
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; in umbels (‘pseudo-umbels’). The ultimate inflorescence unit cymose. Inflorescences scapiflorous; terminal; panicle-derived pseudo-umbels; with involucral bracts. Flowers bracteate; regular; 3 merous; cyclic, or partially acyclic. Sometimes the androecium acyclic. Perigone tube absent.
Perianth with distinct calyx and corolla; 6; free; 2 whorled; isomerous; different in the two whorls; white, or red (inner), or green (outer). Calyx 3; 1 whorled; polysepalous; regular; persistent. Corolla 3; 1 whorled; polypetalous; regular; white, or yellow; deciduous.
Androecium 3, or 6, or 7–100 (i.e. to ‘many’). Androecial members branched, or unbranched; when with trunk bundles, maturing centrifugally; free of the perianth; free of one another, or coherent (then with ‘trunk bundles’). Androecium exclusively of fertile stamens, or including staminodes (the outer members often staminodial). Staminodes external to the fertile stamens. Stamens 3, or 6, or 7–100 (to ‘many’); isomerous with the perianth to polystemonous. Anthers dehiscing via longitudinal slits; extrorse, or latrorse; tetrasporangiate. Endothecium developing fibrous thickenings. The endothecial thickenings girdling. Anther epidermis persistent. Microsporogenesis successive. Anther wall initially with one middle layer; of the ‘monocot’ type. Tapetum amoeboid. Pollen grains aperturate, or nonaperturate; when aperturate, (3–)4–9 aperturate; tri- to poly- foraminate; 3-celled (in all three genera).
Gynoecium 3 carpelled, or 5–9 carpelled, or 12–20 carpelled (all in one whorl). Carpels isomerous with the perianth. Gynoecium apocarpous; eu-apocarpous, or semicarpous (sometimes basally weakly connate); superior. Carpel distally incompletely closed, or fully closed; 12–100 ovuled (‘many’). Placentation dispersed. Ovules over the carpel surface; anatropous to campylotropous; bitegmic; pseudocrassinucellate. Outer integument not contributing to the micropyle. Embryo-sac development Allium-type. Endosperm formation helobial. Embryogeny caryophyllad.
Fruit non-fleshy; an aggregate (in a head). The fruiting carpel dehiscent; a follicle. Seeds non-endospermic. Cotyledons 1. Embryo curved (horseshoe shaped), or bent. Testa without phytomelan.
Seedling. Germination phanerocotylar. Seedling collar not conspicuous. Cotyledon hyperphyll elongated; assimilatory; more or less circular in t.s. Coleoptile absent. Seedling macropodous. First leaf dorsiventral. Primary root ephemeral.
Physiology, biochemistry. Alkaloids absent. Proanthocyanidins absent. Saponins/sapogenins absent.
Geography, cytology. Tropical. Widespread tropical. X = 7, 8, 10 (the chromosomes large).
Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Alismatiflorae; Hydrocharitales. APG 3 core angiosperms; Superorder Lilianae; non-commelinid Monocot; Order Alismatales (as a synonym of Alismataceae?).
Species 12. Genera 3; Butomopsis, Hydrocleys, Limnocharis.
• Technical details: Hydrocleys, Limnocharis.