Herbs, submerged. Stems elongated, branched. Leaves verticillate or lowermost opposite, sessile, linear to narrowly elliptic, margin serrate with 2 small, fringed nodal scales. Plants dioecious or monoecious; flowers unisexual, axillary. Male spathe subsessile, membranous, subglobose, with apical knob and corona of setae, 1-flowered; male flowers shortly pedicellate, free from spathe on water surface at anthesis; sepals 3, ovate or obovate, convex; petals 3, narrower than sepals; stamens 3. Female spathe tubular, sessile, bifid at apex, 1-flowered; sepals and petals similar to male ones; ovary cylindric, attenuate into a filiform beak; styles (2 or)3; ovules few. Fruit cylindric or linear.

One species: temperate to tropical regions.