Submerged aquatics, with slender widely branching stems, and verticillate leaves, the monoecious or dioecious flowers solitary and sessile in the axils. Involucre many-parted, the segments entire or toothed. Perianth none. Stamens numerous, crowded on a flat or convex receptacle; anthers sessile or nearly so, linear-oblong, extrorse, the connective prolonged into a thick appendage beyond the sacs. Pistillate flowers with a superior I-celled ovary; ovule 1, orthotropous, pendulous; style filiform, stigmatic at the summit. Fruit an indehiscent nut or achene. Endosperm none; embryo composed of 4 verticillate oval cotyledons, with a short hypocotyl and a plumule of several nodes and leaves.

The family contains only the following genus.