Monoecious, marsh or aquatic plants, with perennial, creeping rootstocks and erect, terete stems. Leaves alternate, linear or strap-shaped, sheathing at the base, flat, slightly convex on the back. Flowers unisexual, densely crowded in simple, compact, cylindric spikes. Male inflorescence terminal and separated from the female spike or contiguous to it; each spike subtended by spathaceous, usually fugacious, bracts and divided at intervals by smaller caducous bracts. Perianth consisting of bristles. Male flowers with 3, rarely 1—7 stamens; the filaments free or connate; the anthers linear or oblong, basifixed, 2-celled, with longitudinal dehiscence; the connective produced beyond the cells in a conical, carnose acumen; pollen grains simple or compound. Female flowers with a one-celled, superior, stipitate and fusiform ovary; the ovule solitary and anatropous; the style elongate, slender, erect; the stigma ligulate, spathulate, lanceolate or linear. Among the female flowers many sterile ones with clavate tips. Fruit minute, stipitate, fusiform or ellipsoid, with a membranaceous or coriaceous pericarp, splitting longitudinally. Seed subcylindric or narrowly ellipsoid; the testa membranaceous; albumen farinaceous. Embryo cylindric, straight. About 8 species in one genus, widely distributed in temperate and tropical regions.