Leaves ± monomorphic, 10-20 mm, lowest elliptic to spathulate; uppermost in aquatic plants forming a floating rosette with blade elliptic to circular, abruptly contracted into the stalk. Flowers in axils of floating leaves; stamens c. 2 mm; styles 2-3 mm. Fruit 1,6-2 mm, ± orbicular, sessile; mericarps broadly winged on outer surface. Fl. 4-6. Stagnant pools, streams or on exposed damp mud, to 450 m.
Throughout Europe, N. Africa, etc.