Perennial marine or fresh-water plants with floating or submerged leaves, or both. Leaf-blades petioled or sessile, capillary or expanded into a proper blade, or rarely reduced to terete phyllodes. Flowers perfect or monoecious, in sessile or peduncled spikes, or in clusters in the axils of the leaves. Perianth none, but flowers sometimes enclosed in a hyaline sheath. Androecium of 1-4 stamens. Anthers extrorse, 1-2-celled, the connective sometimes becoming perianth-like. Gynoecium of 1-4 distinct, 1-seeded carpels. Fruits mostly nut-like or drupelike, sessile or stipitate. Endosperm wanting.

About 4 genera and 70 species of wide geographic distribution, most abundant in temperate regions. The months noted in the descriptions indicate the fruting period.