Rhizomatous or tuberous, scapose or caulescent, perennial herbs or vines, rarely shrubs, small trees or aquatic herbs; hermaphrodite, monoecious or dioecious; often with milky, watery or pungent sap and tissues rich with crystals of calcium oxalate. Leaves solitary or few, mostly basal; laminae often hastate or sagittate, parallel- or net-veined, sometimes large and fleshy; petioles sheathing. Inflorescence a thick fleshy cylindric spadix, often ± enclosed in a terminal spathe. Flowers minute, actinomorphic, ebracteate, densely crowded over whole, or lower part of spadix, female flowers at base of spadix, male flowers above, occasionally with sterile flowers interspersed, or in a band above both male or female flowers. Spadix with or without terminal sterile appendage. Perianth present in bisexual flowers, segments 4-6, usually lacking in unisexual flowers. Stamens 1-many, free or ± connate; anthers usually 2-celled, opening by pores or slits. Ovaries 1-many, superior, 1-3-(many)-locular with 1-many ovules in each locule; style usually very short, occasionally 0. Fruit a berry, 1-many-seeded. Over 100 genera, mainly of tropics and subtropics but some in temperate regions.

Very small gregarious aquatic perennials, usually < 5 mm long, floating on, or just under, surface of still or slowly moving water, often together forming a complete cover; consisting of ± flattened leafless green platelets, with or without roots, each new platelet arising from a bud in a horizontal pouch on an older platelet. Inflorescence rarely seen, produced in a similar pouch, of 1-2- (3) male flowers maturing successively, and 1 female flower, the whole enclosed within or associated with a membranous spathe. Male flower a single stamen; filament projecting well beyond spathe; pollen sacs 1-2, rounded, splitting transversely; pollen globular. Female flower of rounded ovary and short erect style; carpel single, ovules 1-6, basal. Fruit flattened, sometimes ± winged. Seeds relatively large, smooth or ribbed. Genera 6, widespread in temperate and tropical countries.

Infl. of 1–2–(3) male fls, maturing one after the other, and one female fl., the whole enclosed within or associated with a membr. spathe. ♂ of a single stamen; filament projecting well beyond spathe; pollen sacs 1–2, rounded, splitting transversely; pollen globular. ♀ of rounded ovary and short erect style; carpel single, ovules 1–6, basal. Fr. flattened, sts ± winged. Seeds relatively large, smooth or ribbed with operculum at micropilar end. Very small aquatic herbs floating on or just under the surface of still or slowly moving water, often together forming a complete cover. Lvs absent, the plant consisting of ± flattened, green platelets with or without roots, each platelet arising from a bud in a horizontal pouch on an older platelet; infl. produced in a similar pouch. Genera 4, widespread in temperate and tropical countries.