Submerged aquatic monoecious or dioecious herbs with slender creeping rhizome. Stems capillary, branched. Lvs. alternate or opposite or crowded at nodes, linear, sheathing at base, the sheaths usually ligulate. Fls. minute, axillary, solitary or cymose. Perianth of 3 small free scales or lacking. Stamens 3, 2, or 1; anthers 2, 1-celled, opening lengthwise, Carpels free, 1-9; style short or long, simple or 2-4 lobed; stigma capitate, peltate or spatulate. Fruiting carpels indehiscent, 1-seeded, sessile, stipitate. Seed lacking endosperm.
About 6 genera, widely distributed, in fresh, brackish or salt water. (Munz, Flora So. Calif. 1013).