Slender annuals, rooting at the lower nodes; stems loosely clustered, mostly 1-4 dm, typically wholly submersed; lvs all about alike, dark metallic green, wholly glabrous, mostly 0.5-1.5(-2) cm, to about 1.5 mm wide, 1-nerved, broadest near the base and tapering very gradually to the bifid or broadly notched tip; fls solitary in the axils, without bracteoles; frs mostly 1-2 mm, flattened, suborbicular, the 4 segments more nearly distinct than in our other spp., the 2 major halves separated in life by a broad, deep median furrow extending almost to the commissure, each of these halves also with a deep, narrow commissural groove between the narrow but evident wing-margins; 2n=6. In ponds and slow streams; circumboreal, s. in Amer. to N. Engl., N.Y., Mich., Minn., and Calif. (C. autumnalis)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.