Glabrous biennial to 1 m; lfls ovate, pinnately dissected into linear segments 5-15 mm; peduncles 5-13 cm; rays 7-14, ascending, 2-4 cm; pedicels ascending, 1-12 mm; involucel wanting or nearly so; fr 3-4.5 mm, half as wide, prominently ribbed; 2n=20. Native of Eurasia, sometimes cult. and often established as a weed in waste places; Nf. to B.C., s. to Va., Ind., and Mo., commoner northward. June-Aug.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.