Annual or perennial, monoecious or dioecious, submerged, stoloniferous herbs with short, corm-like or elongated stems. Leaves sessile, radical, spirally arranged or alternate, linear, sheathing or semi-amplexicaul, entire or minutely serrate, acute. Flowers unisexual or bisexual, solitary or males in dioecious plants clustered; female and bisexual ones sessile, males pedicellate, actinomorphic. Spathes tubular, 2-fid at the apex, axillary, sessile or pedunculate, peduncle terete or flattened. Sepals 3, linear or linear-lanceolate, persistent. Petals 3, linear, longer than the sepals, white. Stamens 3-9, free, filaments filiform, anthers linear or lance-shaped, dithecous; staminodes in female flowers absent or minute. Ovary 3-carpelled, syncarpous, linear with a long capillary rostrum; styles 3, connate at the base, undivided at the tips; pistillodes in male flowers 3, slender. Fruit included within the narrow ribbed spathe, linear or linear-lanceolate, 10-many-seeded, membranous walled. Seeds elliptic or fusiform, glabrous or with 3-8 longitudinal lines of ± conspicuous spines or tubercles.