Perennial from a tuberous- thickened base; basal lvs large, long-petioled, reniform or cordate, to 3+ dm wide, callous-dentate or - denticulate, glabrous or nearly so above, arachnoid-tomentose and eventually glabrate beneath; stem 1-4 dm, or to 1 m in fr; heads numerous in a narrow, racemiform infl, the fls purple (rarely whitish), all rayless; invol of male plants 6-8 mm, of female ones 3-4 mm; 2n=60. Native of Europe, escaped from cult. in moist waste places; Mass. to Del., Pa., and Ill. Apr., May.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.