L., Syst. Nat. ed.10,1270.1759 Glabrous, monoecious, aquatic herb, usually 1-1.5 m tall. Leaves basal; petioles fleshy, vaginate in lower third, becoming terete above, usually longer than blades; blades lanceolate to elliptic, gradually tapered to both ends, mostly 25-40 cm long, 4.5-10 cm wide. Inflorescences held above leaves, usually branched; flowers in whorls of 3 at each node, those at the lower nodes usually pistillate, those at the upper nodes staminate; bracts 3 at each node, lanceolate, 5-20 mm long; pedicels 1-3 cm long, ascending; sepals 3, ovate, to 1 cm long; petals 3, obovate, white, to 1.3 cm long, spreading at anthesis; stamens many; filaments free, pubescent in lower half. Fruit a cluster of numerous achenes, the clusters depressed-globose, ca 1 cm wide; achenes +/- flattened, oblique, beaked at apex, to 2.5 mm long. Croat 8446. Uncommon, but locally abundant in marshes. Flowers and fruits November to July, principally March to July. Seeds are probably dispersed by small shorebirds, though many are no doubt spilled locally.