C. aquatica: aquatic; stems slender, glabrous, floating in water, or creeping and rooting in wet mud; leaves obovate or oblong, or the lower submerged ones narrow-linear, and obtuse or notched at the top: the upper ones obovate, and spreading in little tufts on the surface of the water, or all submerged and linear; flowers minute, the males consisting of a single stamen with a conspicuous filament, the females of a sessile or stalked ovary, with two erect or recurved styles. - Shallow waters or wet mud. Fl. May to September.