Glabrous annual; lvs narrowly subulate, 1-5 cm; scape 2-10 cm, with 2-10 rather remote fls; sep ±persistent in fr; frs 2-4 mm, short-stipitate, elliptic to broadly obovate, on ascending pedicels; 2n=28. Submerged along the margins of fresh-water ponds and lakes, less often on muddy shores; circumboreal, s. in Amer. to Me., Vt., Minn., Wyo., and Calif. June-Aug. Amer. pls are var. americana (G. A. Mulligan & Calder) B. Boivin.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.