Delicate, freely branched, glabrous or subglabrous annual; stems 1-2 dm, decumbent to prostrate, much-branched from the base; basal and cauline lvs short-petiolate, neither clasping nor auriculate, oblong to oblanceolate or spatulate, mostly 2-6 נ1-1.5 cm, usually lyrate- pinnatifid; pet ca 1 mm or less, a little shorter than the sep; mature pedicels 1.5-3.5 mm, ascending; frs cylindric, straight or incurved, sometimes constricted at the middle, mostly 3-8 נ1-1.5 mm; seeds ca 20-70. Wet, disturbed places; widely scattered in w. U.S. and adj. Can. and Mex., e. occasionally to St. Louis. (R. obtusa, misapplied; R. truncata)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.