Distribution: Occurring on both sides of the Cascades crest in Washington; widely distributed throughout much of North America.
Habitat: Fresh to brackish, standing to slow-flowing water, sea level to moderate elevations in the mountains.
Conservation Status: Not of concern
Monoecious, submersed, aquatic perennials from slender rhizomes, the stems nearly filiform, freely branching.
Leaves opposite, hair-like, 1-nerved, 2-10 cm. long; stipules free, membranous.
Flowers naked, axillary, the staminate and pistillate usually in the same axil; staminate flowers a single stamen, the slender filament much exceeding the pistil; pistillate flowers of 2-8 distinct carpels; style short, stigma peltate.
Achenes sickle-shaped, 3-4 mm. long, compressed and keeled, with a short stipe and slender stylar beak 1 mm. long.