C. demersum: aquatic; stems floating, submersed; leaves whorled, twice or thrice forked, with subulate segments, usually slightly-toothed on the edge; flowers small, sessile, axillary, without any real perianth, the males consisting of 12 - 20 sessile, oblong anthers, the females of a small ovary with a simple style. - Pools, slow streams, and shallow lakes. Fl. June, July.