Fls unisexual, minute, densely crowded on large cylindric infl. of which the lower part is wholly female, the upper, short-lived, terminal part male, the two parts sts separated by a length of bare stem; spathes, one to each portion of infl., membr. and caducous. Male fl. of 1-few anthers on ± fused filaments associated with simple or forked hairs or narrow bracteoles; anthers linear, basifixed; connective produced into an obtuse or subulate fleshy apex; pollen grains single or remaining in tetrads. Female fls grouped on simple or compound pedicels, with or without bracteoles; each fl. of a narrow one-celled ovary, a slender style and elongated stigma, the whole surrounded by long hairs borne on a gynophore that often elongates as fr. matures; sterile fls sts ∞ on upper part of compound pedicels, the aborted ovary (carpodium) clavate and almost terminal. Fr. dry, dispersed with persistent style and hairy gynophore, at length splitting to liberate narrow endospermous seed. Marsh or aquatic perennials with creeping rhizomes and simple stems often submerged at base. Lvs tufted, distichous, linear, glab.; sheath open; lamina thick and ± spongy. One cosmopolitan genus of some 10 spp.