Plants with a short stout rhizome or caudex, sometimes with short thick stolons as well; stem stout, 0.5-2.5 m, simple or much branched above, uniformly spreading-hairy at least under the heads, conspicuously spreading-hispid (or occasionally glabrous) below; lvs chiefly cauline, sessile, auriculate-clasping, rather distantly serrate to occasionally entire, scabrous to subglabrous above, glabrous or spreading-hairy along the midrib beneath, lanceolate to oblong or elliptic-oblong, 7-16 cm נ12-40 mm; heads few to many in a leafy infl; invol 6-12 mm, its bracts slender and loose, scarcely or not at all imbricate, at least the inner long-acuminate to attenuate, often some of the outer enlarged and leafy, but still narrow; rays 30-60, blue (rose or white), 7-18 mm; achenes glabrous or nearly so; 2n=16. Swamps and other moist places; Nf. to Sask., s. to Va., Ill., and Neb., and in the mts. to Ga. and Ala.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.