Vallisneria verticillata Roxb.
Caulescent, glabrous, profusely branched freshwater herb with 5-50 mm long internodes and fibrous roots at some nodes. Leaves oblong-linear to lanceolate, (8-) 10-40 (-50) mm long, (1-) 2-3 mm wide, green, margin serrate-dentate, apex acute-apiculate; nodal scales 2, axillary, membranous with orange brown cilia on margin. Male spathe 1.25-1.50 mm long, bursting open to liberate male flower, beset with subulate appendages. Male flower: sepals reflexed, 1.5-3 mm long; petals linear-spathulate, equalling the sepals, patent or reflexed, obtuse; stamens with minute filaments. Female spathe c. 5 mm long, reddish-brown striped, bidentate. Ovary oblong, 3.4 mm long, with 1.5-10 cm long slender rostrum. Fruit ± terete. 5-7 mm long. Seeds dark brown, c. 2.5 mm long.
Fl. Per.: October-January.
Lectotype: “Habitat in India”, Herb. Linn. 1106. 1 (LINN).
Distribution: Gregarious in ditches, pools, lakes, wet ricefields and slow-running water streams in S.E. Europe, Africa, Asia and Australia from sea level to 6000'; introduced in America and elsewhere.
The plant is eaten by some fresh water fish and may be used as manure wherever it occurs in large quantities. It becomes a serious menace to navigation in large lakes and in irrigation canals as it reduces the rate of flow of water.