S. ramosum: aquatic; leaves long, linear, sheathing at the base; stems erect, two feet high or more, with a few branches at the summit, each bearing several smaller male heads, and below them a few larger female heads, which are glabrous with prominent stigmas. - Margins of ponds, lakes, and streams. Fl. July.
S. simplex is rather smaller, with narrower leaves, the flower-heads much fewer towards the top of the simple stem; and S. natans has weaker stems, long narrow floating leaves, and very few flower-heads.