Herbaceous aquatic annuals or perennials, rooted in mud or free-floating. Stems of two types, vegetative and flowering; vegetative stem indeterminate, containing many leaves, glabrous; flowering stem determinate, containing a single leaf, spathe, and terminal infloresence. Leaves alternate, composed of a strongly sheathing base, petiole (excluding sessile leaves), and lamina; stipules marcescent, transparent, truncate at apex, sheathing, opposite petiolate leaf base, or absent (on species with only sessile leaves). Inflorescence a panicle, spike, or monoflorous; peduncle glabrous to glandular-pubescent, subtending spathe bract-like, folded, glabrous, with an acute to caudate apex. Flowers trimerous, bisexual, zygomorphic, sessile, glandular-pubescent or pilose; perianth consisting of six petaloid, oblong to oblanceolate tepals, basally fused into a tube; stamens 6, adnate to the perianth, filaments pubescent with multicellular or glandular hairs, the anthers rounded; ovary superior, trilocular, with 1 or 3 locules developing to maturity, placentation parietal or basal, ovules one to many, style pubescent with multicellular hairs or glabrous, stigma entire or 3-lobedwith single-celled hairs. Fruit a many-seeded capsule with persistent unmodified perianth or a nutlet with thickened, ridged perianth; seeds longitudinally winged or smooth.