Small, floating or submerged, monoecious, aquatic herbs, consisting of a flat or subglobular, green, often leaf-like cladode. Reproduction is usually vegetative; in the posterior portion, on either side or centrally, is a groove or pouch under the edge, in which arise branches which later become detached and form new plants. Flowers unisexual, very rarely observed. Perianth absent. Stamens 1–2. Ovary 1-locular; style simple. 5 gen., temp. and trop.; fresh water.