Annual or perennial, amphibious herbs with laticiferous ducts. Rhizome mostly stout, short, with adventitious fibrous roots. Leaves radical, rosetted, erect or floating with vaginate petiole, rarely floating or submerged and reduced to phyllodes, lamina linear-lanceolate to sagittate, rarely ribbon shaped or broadly elliptic to ovate, with parallel convergent venation and hydathodes. Inflorescence simple or compound, scapose, raceme or panicle with verticelled flowers and branches; peduncle mostly spongy, rarely hollow. Flowers small, bisexual or more rarely unisexual, actinomorphic, trimerous, hypogynous. Bracts 3 rarely 2 per whorl of flowers or branches. Thalamus flat to globose. Sepals 3, free, green, imbricate, persistent. Petals 3, free, mostly white rarely pink, fugacious, imbricate, rarely absent. Stamens 3-many, free, filaments flattened or filiform, anthers basifixed or rarely versatile, dithecous, dehiscing longitudinally. Carpels 3-many, whorled or spiral, apocarpous or occasionally basally connate; ovaries superior, sessile or stipitate, unilocular, each with 1, rarely 2 or more erect, campylotropous or anatropous ovules; styles terminal or ventral, stigma simple. Fruit a head (etaerio) of free achenes or rarely basally united follicles. Seeds oblong or curved, with membranous, smooth, wrinkled or ridged testa, exalbuminous; embryo curved, hippocrepiform.