H. Morsus-ranae: aquatic; stems floating, runner-like, with tufts of thick, entire, stalked, orbicular-cordate leaves; flowers dioecious: the males on short peduncles, bearing 2-3 flowers on long pedicels, enclosed at the base in a spathe of two thin bracts, each flower with the outer segments pale-green, the inner ones large white, and having 3-12 stamens; the females resembling the males, but with the spathe sessile among the leaves, and the flowers with six styles having 2-cleft stigmas. - Ditches and ponds. Fl. July, August.