Distribution: Widely distributed on both sides of the Cascades in Washington; Alaska to south California and New Mexico, east through southern Canada and the northern states to Maine.
Habitat: Streams, ponds and shallow lakes, generally at least partially emerged.
Conservation Status: Not of concern
Glabrous, aquatic perennials with creeping rhizomes, the erect branches partly emersed, 1.5-2.5 mm. thick and 5-30 cm. long, usually simple, but frequently with short branches from the lower nodes.
Leaves linear, entire, 6-12 per whorl, 1-2 mm. broad and 10-35 mm. long.
Flowers mostly perfect, sessile and solitary in the leaf axils; perianth none; stamen 1; pistil 1-celled; style slender, stigmatic the entire length, lying in the groove between the lobes of the large anther.
Fruit nut-like, 1-seeded.