Distribution
Ukraine (introduced)

Native to: Alabama, Arkansas, British Columbia, California, Colorado, Connecticut, Delaware, Florida, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Manitoba, Maryland, Masachusettes, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Brunswick, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Nova Scotia, Ohio, Ontario, Oregon, Pennsylvania, Québec, Rhode I., Saskatchewan, South Dakota, Tennessee, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, Wyoming.
Introduced into: Austria, Baltic States, Belarus, Belgium, Bulgaria, Buryatiya, Canary Is., Central European Rus, Cuba, Czechoslovakia, Denmark, East European Russia, Egypt, Finland, France, Germany, Great Britain, Greece, Hungary, Ireland, Irkutsk, Italy, Jamaica, Krasnoyarsk, Krym, Morocco, Netherlands, New South Wales, New Zealand North, New Zealand South, North European Russi, Northwest European R, Norway, Palestine, Poland, Portugal, Puerto Rico, Romania, South European Russi, Spain, Sweden, Switzerland, Transcaucasus, Turkey-in-Europe, Ukraine, West Siberia, Yugoslavia.

Leaves mostly in 3s, spreading to recurved, linear, oblong, to ovate, 5-13 x (1.1-)2-5 mm, flat. Inflorescences: staminate spathes cylindric, 8.2-13.5 mm; peduncles abscissing just before or during anthesis; pistillate spathes cylindric, 8.3-17.5 mm. Flowers unisexual; staminate flowers: stamens 7-9(-18), pedicels detaching before or during anthesis; all filaments connate proximally, forming column; anthers 1.7-3 mm; pollen in tetrads; pistillate flowers: styles 2.6-4 mm. Seeds fusiform, 4-5.7 mm, basal hairs absent. 2n = 24 (Britain).
Flowering summer. Waters, mostly calcareous, of lakes and rivers; 0-2000 m.