Submerged, dioecious, stoloniferous, glabrous, short-stemmed, perennial herbs with fibrous roots. Leaves radical, sessile, linear, ribbon-shaped, parallel-sided, entire or faintly dentate, obtuse. Flowers unisexual, female solitary, males numerous. Male spathe ovoid, 3-fid at the tip, shortly pedunculate. Male flowers pedicellate, minute, breaking off and floating on the water surface; sepals 3, ovate or oblong-ovate, petaloid; petals 3, minute or absent; stamens 1-3, anthers didymous; pistillode absent. Female spathe tubular, bifid on long slender peduncle that spirally coils after fertilization. Female flower: sepals and petals as in the male; ovary inferior, sessile, linear, unilocular with 3 parietal placentae; styles 3, each 2-lobed with hairs on the innerside; staminodes 3, each bifid. Furit linear, cylindric, 5-10 cm long, included within the spathe. Seeds oblong to fusiform, with membranous testa.