Submerged perennial. Stems thick, 30-150 cm long, branched, glabrous, rhizome rooting. Leaves 10-25 mm long, pectinate, with 20-26 segments. Spikes terminal, 50-70 mm long, with flowers in whorls of 4 in the axils of bracts; the upper flowers male, the lower female. Bracts 1.5-3 mm long, the upper obovate, entire; the lower: pinnatifid or with a deeply cleft margin. Male flower : sepals 0.5-1 mm long, triangular, obtuse; petals 2 mm long, oblong, cucullate, reddish. Stamens 8, filaments short; anthers 1-1.5 mm long. Female flower: calyx c. 1.5 mm long; petals minute. Ovary c. 1.5 mm long, subglobose; styles short, stigmas plumose. Fruit 2 mm long, subglobose.