Stems hollow, rooting from the lower nodes, to 1 m, ascending; cauline lvs with dilated, sheathing petiole and well defined, lanceolate blade to 15 × 3 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)