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Herbs, perennial, aquatic or in marshes, with creeping rhizomes. Stems simple or branched, robust or slender. Leaves alternate, distichous, emergent or floating, sheathed at base. Flowers minute, densely crowded in globose heads on upper part of stems and branches; several male and female heads in panicle, raceme, or spike, male heads above female. Perianth segments of 3-6 chaffy elongate scales. Male flowers with 3 or more stamens; anthers basifixed, longitudinally dehiscent; filaments free or partly united. Female flowers bracteolate; ovary 1-loculed or rarely 2-loculed, narrow at base; styles simple or forked, with a unilateral stigma; ovule 1, pendulous. Fruit nutlike, indehiscent.
Herbs, erect or floating, or sometimes with some leaves floating and some emergent. Leaves flat, plano-convex, or abaxially keeled and V-shaped in section, spongy, margins entire. Flowers wind-pollinated, odorless, sessile. Fruits sessile or stipitate; tepals persistent, attached at base, in one species partially adnate to stipe. Seeds 1--2(--3), slender-ovoid; coat thin, appressed to endocarp. x = 15.
Characters of the family. 15, mainly N. Temp.
Characters as for the family.
