Distribution
Albania, Algeria, Austria, Belarus, Belgium, Bulgaria, Cyprus, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, India, Iran, Iraq, Ireland, Italy, Japan, Kazakhstan, Libya, Mongolia, Morocco, Nepal, Netherlands, Norway, Pakistan, Poland, Portugal, Romania, Spain, Sweden, Switzerland, Tunisia, Turkey, Turkmenistan, Ukraine, Uzbekistan, Vietnam

Native to: Afghanistan, Alaska, Albania, Algeria, Altay, Amur, Arizona, Austria, Azores, Baleares, Baltic States, Belarus, Belgium, British Columbia, Bulgaria, Buryatiya, Canary Is., Central European Rus, China North-Central, China South-Central, China Southeast, Chita, Colorado, Connecticut, Corse, Cyprus, Czechoslovakia, Denmark, East Aegean Is., East European Russia, East Himalaya, Finland, France, Føroyar, Germany, Great Britain, Greece, Hungary, Iceland, Idaho, Illinois, India, Indiana, Inner Mongolia, Iran, Iraq, Ireland, Irkutsk, Italy, Japan, Kamchatka, Kazakhstan, Kentucky, Khabarovsk, Kirgizstan, Korea, Krasnoyarsk, Kriti, Kuril Is., Labrador, Lebanon-Syria, Libya, Madeira, Maine, Manchuria, Masachusettes, Mexico Northeast, Mexico Northwest, Michigan, Minnesota, Mongolia, Morocco, Nebraska, Nepal, Netherlands, Nevada, New Brunswick, New Hampshire, New Jersey, New Mexico, New York, Newfoundland, North Carolina, North Caucasus, North European Russi, Northwest European R, Norway, Ohio, Ontario, Oregon, Pakistan, Palestine, Pennsylvania, Poland, Portugal, Primorye, Prince Edward I., Qinghai, Québec, Rhode I., Romania, Sakhalin, Sardegna, Sicilia, South Dakota, South European Russi, Spain, Sweden, Switzerland, Tadzhikistan, Tibet, Transcaucasus, Tunisia, Turkey, Turkey-in-Europe, Turkmenistan, Tuva, Ukraine, Utah, Uzbekistan, Vermont, Vietnam, Virginia, Washington, West Himalaya, West Siberia, West Virginia, Xinjiang, Yakutskiya, Yugoslavia.
Introduced into: Antipodean Is., Chatham Is., New South Wales, New Zealand North, New Zealand South, Norfolk Is., Peru, South Australia, Tristan da Cunha, Victoria, Western Australia.

Herbs, perennial, rhizomatous to nearly cespitose, 0.5-6(-10) dm. Rhizomes 2-3 mm diam., not swollen. Culms erect to decumbent (and floating), terete, 1-3 mm diam., smooth. Cataphylls 1, maroon to straw-colored, apex acute to obtuse. Leaves: basal 0-2, cauline (1-)3-6; auricles 0.5-1 mm, apex rounded, scarious; blade green to straw-colored, terete, 3.5-12 cm x 0.5-1.1 mm. Inflorescences terminal panicles of 3-30(-50) heads, 3.5-8 cm, branches spreading; primary bract erect; heads 3-10-flowered, obpyramidal to hemispheric, 6-8 mm diam. Flowers: tepals green to straw-colored or dark brown, ovate to lanceolate, 1.8-3 mm; outer tepals with apex acute or acuminate; inner tepals with apex acute acuminate to obtuse; stamens 6, anthers equal to filament length. Capsules exserted ca. 1 mm beyond perianth, chestnut brown to dark brown, imperfectly 3-locular, ellipsoid or ovoid, 2.8-4 mm, apex acute proximal to beak, valves separating at dehiscence. Seeds obovoid, 0.5 mm, not tailed. 2n = 80.
Fruiting mid summer-fall. Wet ground in ditches, lake and stream margins, and a variety of other habitats, often a calciphile; 0-3000 m.