Erect annual, 2-6 dm, often branched, with hairy herbage; lvs all or mostly opposite, petiolate, linear to ovate, coarsely toothed to subentire; infl congested, mingled with reduced green lvs; involucres 2-3 mm, with fimbriate lobes and a conspicuous, fleshy, flattened-obconic, tangentially bilabiate gland; styles bifid half their length, or deeper; fr smooth, 5 mm thick; seeds ovoid, rough-tuberculate, 2.5-3 mm, usually carunculate; 2n=14(?), 28, 56. Dry soil; Ill. and Wis. to Wyo. and Mex., and established as a weed on roadsides and waste places, especially in cindery soil, e to Mass., N.Y. and Va. July-Sept. (Poinsettia d.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.