Annual or perennial herbs, aquatic or growing in swamps or marshes. Rhizome sometimes with tuberous roots. Leaves mostly basal, linear, sheathing at the base, sometimes floating. Flowers bisexual, regular, small, on scapes in spikes or racemes; bracts absent. Perianth segments 6, in 2 whorls, greenish or reddish, deciduous. Stamens 3–6, subsessile. Carpels 2–6, free or basally connate or cohering. Fruit cylindrical or obovoid, consisting of free or connate follicles. 4 gen., mainly temp. S. hemisphere.