Distribution: Occurring chiefly west of the Cascades crest along the coastal counties in Washington; British Columbia to Baja California, Mexico, east to the Rocky Mountains and northern Great Plains; also in South America.
Habitat: Generally in shallow water, but often stranded in mud at edge of receding ponds, coastal tideflats to interior valleys.
Conservation Status: Not of concern
Tufted annual, submerged in youth, sometimes becoming emergent in age, glabrous, from fibrous roots.
Leaves basal, 5-20 cm long and 1-5 mm broad, somewhat elliptic or round in cross section; sheath membranous; ligule approximately 1 mm, tip generally obtuse or notched.
Inflorescence scapose, dense spike of bisexual and occasionally staminate flowers, typically emergent, 6-20 cm, also with submersed sessile pistillate flowers enclosed in leaf sheath at base of scape.
Achene 2-10 mm, ribbed, generally flat, somewhat winged in bisexual flowers, angled in pistillate flowers, tip truncate with off-center beak.