Stems 1-2.5 m, square; lvs or their petiolar bases connate- perfoliate, the blade deltoid to ovate, coarsely toothed, to 3 נ1.5 dm; heads in an open infl, the disk 1.5-2.5 cm wide; invol 12-25 mm, its bracts elliptic or ovate, subequal or the outer longer, rays 1.5-4 cm; 2n=14. Woods and low ground; s. Ont. to N.D., s. to N.C., Miss., La., and Okla., and intr. into N. Engl. July-Sept. Two vars.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.