Distribution: Occurring on both sides of the Cascades crest in Washington; British Columbia to California, east to Idaho; native from the Great Plains to the Atlantic Coast; also in Eurasia.

Habitat: Shallow, quiet to slow-moving water.

Flowers: May-August

Origin: Introduced from Europe and/or eastern North America

Growth Duration: Perennial

Conservation Status: Not of concern

Pollination: Wind

Monoecious, perennial herbs of wet places from extensive rhizomes, the stems up to 1.5 m. tall, erect, cylindrical and pithy.

Leaves alternate, sheathing, linear, the blades 3-10 mm. broad, deep green, convex on the outer surface.

Flowers naked in terminal, cylindrical, spike-like inflorescences, the staminate above the pistillate, the two portions separated by 0.5-4 cm.; staminate flowers consisting of 2-5 stamens borne directly on the main axis, intermixed with slender hairs; pistillate flowers a single, 1-celled pistil, subtended by a linear bract dilated at the tip; pistillate section up to 15 mm. thick, brown; abortive ovaries flattened, wedge-shaped.

Fruit dry, 1 mm. long, ellipsoid.