Rhizomatous aquatic. Stem branched or simple. Leaves submerged, sessile, lanceolate to orbicular, cordate-amplexicaul, size and shape variable 2-6 cm long, 1.5-2 (-2.5) cm broad, entire or minutely denticulate, rounded to obtuse at the apex, usually alternate below, opposite above, 2-7 (-13)-veined, thin, translucent. Stipules free, small, length variable, less than 1 cm long, soon evanescent. Spike 4-5 cm long, densely flowered. Fruitlets 2-3.5 mm long, 1.5-2 (-3) mm broad, beaked, ventral area convex, irregular or straight, beak more or less keeled.
Fl. Per.: November-March.
Type: Habitat in Europae lacubus fluviisque argillosis (Sweden), Herb. Linn. no. 175/3 (LINN).
Distribution: Europe, Asia, Africa, N. America and Australia.
Fruitlet polymorphism has been noticed in this species (Aalto, l.c.). Plants are generally used in manuring and the rootstocks are used as food for animals.
