Perennial freshwater herbs; monoclinous, monoecious or dioecious, with tuber or rhizome, stolon or corm and erect stem; entomophilous via beetles or bees, or cleistogamous; with milky sap and raised glands or punctae. Leaves simple, sheathing at base, alternate, petiolate or sessile, often containing hydropoten (localised regions of flat cells appearing as blotches), floating, floating and submersed, or all submersed; blades with parallel venation, main veins connected by cross veins, margins often bounded by a thin parallel vein; tissue between veins may disintegrate with age, leaving a network of veins separated by holes; axillary scales present. Inflorescence pedunculate, spadix subtended by a caducous or persistent spathe, branched or single, floating, projected above the water or remaining submerged. Flowers sessile, zygomorphic, perfect or imperfect; perianth in one whorl of 1–6 parts or absent, persistent, white to pink, yellow, green-blue or violet; stamens 6–18(–50), 2-loculed, dehiscing by longitudinal slits; carpels separate, 2–6(–9), superior, sessile, placentation basal. Fruit a follicle, with terminal, lateral, curved or straight beak. Seeds with straight embryo, lacking endosperm, with single or double testa.