Fls unisexual, small, densely crowded in separate globose capitula, spaced out on simple or branched infls; lower capitula female, each in or above the axil of a lfy bract, stalked or sessile; higher capitula male, bractless or with small bract, falling after anthesis. Per. of 3–8 chaffy ± spathulate scales, larger in ♀. Male fl. with 3 or more stamens; filaments ± united; anthers oblong, basifixed. Female fl. with ovary sessile with narrow base, us. unilocular; ovule solitary, pendulous; style us. simple, sts forked, stigma obliquely terminal. Fr. dry, indehiscent, with spongy exocarp and hard endocarp; style base forming beak. Seed with straight embryo in mealy endosperm. Marsh or aquatic perennial herbs, with creeping rhizomes and stems often submerged at base. Lvs alt., erect or floating, elongate-linear, glab.; sheath open; lamina ± keeled. One genus of some 15–20 spp., widespread.