Amphibious monoecious herb. Aquatic form with long branched stems bearing floating rosettes and submerged lvs; terrestrial form with creeping stems and ascending branches. Submerged lvs 6-30 × 0.5-2.5 mm, linear, 1-nerved; apex 2-toothed; rosette lvs 0.4-1 cm long, spathulate, 3-nerved, occasionally with a small extra vein outside; lvs of terrestrial form linear-elliptic to elliptic, 1-(3)-nerved. ♂ and ♀ fls solitary in axils of rosette lvs; bracteoles usually 0. Stamens c. 1 mm long; anthers c. 0.5 mm long. Fr. usually sessile, occasionally pedicellate, 1.2-1.4 mm diam., suborbicular; mericarp-faces flat; wing very narrow, often white, usually running right round mericarp; commissural groove wide and shallow.