Description from Flora of China
Herbs, perennial, in marshes or aquatic, with creeping rhizomes. Leaves alternate, erect, distichous, linear, usually spongy, margin entire, sheathed at base. Flowers unisexual, minute, numerous, densely crowded in a cylindric spike with lower part female and upper part male; bracts leaflike. Perianth absent. Male flowers consisting of 1-3 stamens usually connate at base of filaments, surrounded by hairs; anthers 2-thecous, basifixed, longitudinally dehiscent; filaments short; pollen grains in monads or tetrads. Female flowers: ovary 1-loculed, on a long capillary stalk with many fine hairs or bracteoles at base; styles capillary; stigmas broadened or spatulate; ovule 1; sterile ovary without style. Fruit minute, falling off together with stalk.
About 16 species: tropical and temperate regions; 12 species (three endemic) in China.