The family can be distinguished by predominantly marshy or aquatic herbs. Roots fibrous from stout rhizome. Leaves floating, basal , long-petioled, sheathing basally, the blades very  variable from linear to ovate or the bases sagittate or hastate, reticulately veined; inflorescence a raceme or panicle. Flowers bisexual (rarely unisexual), pedicelled, often in whorls, bracteate,. Perianth 2 seriate, 6,  free segments in 2 series, regular. Stamens 6, hypogynous, free, the anthers 2-celled, extrorse or dehiscing by lateral slits. Gynoecium of numerous free pistils, spirally arranged or in advanced genera in a single whorl. Ovary superior, unilocular, the ovules solitary or infrequently several, basal or nearly so, the style mostly acicular and persistent, the stigma 1, fruit an achene, rarely follicular and then dehiscing basically.