Stems hollow, rooting from the lower nodes, to 1 m, ascending; cauline lvs with dilated, sheathing petiole and well defined, lanceolate blade to 15 נ3 cm, usually denticulate; pet 5-10 mm, equaling or a little exceeding the sep; achenes 1.5-2 mm, the horizontal beak 1-1.3 mm. Swamps, marshes, and shores, mostly in heavy soil; Me. to Minn., s. to Va., Tenn., and La. June-Sept. (R. obtusiusculus Raf., probably misapplied)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.