Small, submerged, dioecious, perennial herb forming large masses; stems slender, long, 5-50 cm or more, branched, flaccid, often rooting at nodes; leaves usually 4-8 in a whorl, small, sessile, linear-oblong, entire or serrulate, midrib strong; flowers minute, solitary, unisexual; male flowers shortly pedicelled, spathe subglobose, muricate, sessile; sepals-3, ovate or obovate, green; petals-3, green, very variable; stamens 3, anthers large, kidney shaped, filaments filiform; pistillode minute; female flowers sessile, 1 or 2 in tubular, 2-toothed spathe; sepals and petals as in males but narrower; ovary produced beyond in a filiform beak, 1 to 10 locular, styles 2-3, linear, stigmas-3, fimbriate; fruits indehiscent, membranous or fleshy, smooth or muricate; seeds 2-3, oblong .