Sonchus asper (L.) Hill
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Much like no. 2 [Sonchus oleraceus L.] commonly more prickly; lvs pinnatifid, or frequently obovate and lobeless, with rounded and conspicuously prickly-toothed, not acute auricles; cor-tube somewhat longer than the ligule; achenes flatter, with 3(4–5) evident ribs on each face, not rugulose, although there may be minute projections from the marginal ribs; 2n=18. A cosmopolitan weed, native to Europe. July–Oct.