Distribution: Occurring on both sides of the Cascades crest in Washington; Alaska south to California, across the northern half of North America to the Atlantic Coast.
Habitat: Shallow water, mostly in mountain lakes, sometimes completely submersed.
Conservation Status: Not of concern
Dioecious, aquatic perennials from rhizomes, stems from floating and up to 10 dm. long to largely emersed and 1-3 dm. tall.
Leaves floating to erect, 3-6 mm. broad, exceeding the inflorescence.
Flowers in globose clusters toward the tip of the main stem; inflorescence simple, up to 6 cm. long, with 3-4 heads, the uppermost staminate or with both staminate and pistillate flowers; pistillate heads up to 12 mm. thick when mature, usually all sessile; stamens 3-5 with 3-5 minute, chaffy bracts; pistil 1, stigma 1.
Fruit a nutlet-like achene with a stipe 1 mm. long, the body ellipsoid, 3 mm. long, the beak 1-1.5 mm. long.