Aquatic, scapose, perennial herbs, with globose tubers. Leaves floating or erect, usually long-petioled. Inflorescence of 1-2-(5) spikes, often enclosed at first in a caducous sheath. Flowers bisexual, rarely unisexual; segments 3-1 or 0, petaloid or bract-like, usually persistent. Stamens 5-18, free, hypogynous; filaments usually flattened; anthers 2-celled, dehiscing by longitudinal slits. Carpels 2-6, free, superior, sessile. Ovules 2 or more, basal. Fruit of 3-(8) hardened follicles. Seeds 4-8, oblong or cylindric. One genus, in the tropics of the Old World and in S. Africa.