Research Studies of the State College of Washington 30(2): 23. 1962.
Leaves sometimes in 2s, spreading, linear to narrowly elliptic, 4.7–24.8 × (0.8–)1.8–4.3 mm, flat. Inflorescences: staminate spathes cylindric, 10.2–42 mm; peduncles abscissing following anthesis; pistillate spathes linear, 9–67 mm. Flowers unisexual; staminate flowers: stamens 7–9; pedicels remaining briefly following anthesis; inner 3 filaments connate proximally, forming column; anthers 3–4.5 mm; pollen in monads; pistillate flowers: styles 2.3–3 mm. Seeds ellipsoid, 2.8–3 mm, densely covered with long hairs.
Phenology: Flowering summer–fall.
Habitat: Waters of rivers and reservoirs
Elevation: 100–2500 m
Alta., B.C., Man., Sask., Colo., Idaho, Kans., Minn., Mont., N.Mex., N.Dak., Oreg., S.Dak., Utah, Wyo.