Erect, glabrous, rhizomatous, terrestrial, water- and swamp herbs, laticiferous (Butomus excepted). Leaves radical, sheathing, curvinerved (cauline in Hydrocleis), leaf-blades above water (Hydrocleis excepted). Flowers umbellate (or solitary), actinomorphic, ♀♂. Perianth 2-seriate. Sepals 3, imbricate, mostly persistent, usually green. Petals 3, imbricate, usually thin, fugacious (persistent in Butomus). Stamens 8-9 or ~, rarely less, sometimes the outer ones staminodial, filaments flattened, free; anthers basifixed, 2-celled, opening lengthwise with lateral slits. Gynoecium apocarpous, superior; carpels 6- ~, rarely less by reduction, in a whorl, free or cohering only at the base, dehiscing with an adaxial slit. Ovules ~, anatropous, scattered on reticulately branched placentas. Fruitlets ~-spermous, at last dehiscing along the ventral (adaxial) side. Seeds ~; embryo flat and horse-shoe shaped (elliptic-terete and straight in Butomus); endosperm 0. Distr. Less than 10 spp. belonging to 5 genera, in temperate and tropical regions, absent from Africa S of the equator, in Malaysia one native and one introduced genus both represented by one species.