Distribution: Alaska south to California, east to Colorado.
Habitat: Shallow ponds and marshes.
Flowers: June - September
Conservation Status: Not of concern
Dioecious, aquatic perennials from rhizomes, the stems erect, 2-4 dm. tall.
Leaves alternate, linear, mostly emersed and erect, sometimes partially submersed or floating, 2-5 dm. long and 6-12 mm. broad, from slightly keeled to triangular, usually expanded and scarious-margined toward the base.
Flowers in globose clusters toward the tip of the main stem; inflorescence simple, with 3-5 pistillate heads below a like number of staminate heads, the pistillate heads up to 3 cm. thick, the lower ones axillary to leaf-like bracts on peduncles up to 12 cm. long; stamens 3-5 with 3-5 minute, chaffy bracts, the filaments long; pistil 1, the stigma linear, 1.5-2 mm. long.
Achenes spindle-shaped, 4-5 mm. long, narrowed to a stylar beak 3-4 mm. long, on a stipe 2.5-3.5 mm. long.