Aquatic often rather large perennial herbs with creeping, subterranean stolons. Stem simple or branched, leafy at the base, stiff or flaccid, erect or floating, bearing a terminal spike or panicle. Leaves long, linear from a sheathing base. Flowers (♂♀), crowded in separate globose clusters; lower clusters ♀, in or above the axil of a leafy bract, stalked or sessile; higher clusters ♂, bractless or with a small bract. ♂: Perianth actinomorphic, choriphyllous. Tepals 3(-6), spathulate. Stamens 3(-6); filaments free or connate at the base; anthers basifixed, oblong; pollen globose. ♀: Tepals as in ♂ but larger. Ovary 1, exceptionally 2, sessile with a narrow base, unilocular; ovule 1, pendulous; style 1, usually simple, rarely forked; stigma ...