Stems flaccid, prostrate and creeping, or partly floating; lvs 0.5-3 cm, lanceolate to ovate, abruptly narrowed to a petiole about as long; fls minute, sessile, 4-merous, apetalous; fr oblong-obovoid, 3-4 mm, roundly 4-sided, the wall much thickened and corky below each sep, very thin below each sinus and revealing the outline of the seeds when dry; bracteoles minute or wanting; 2n=16. Creeping on mud and partly floating in shallow water; widespread in the n. hemisphere, and throughout our range.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.