Colonial by long rhizomes; stems 6-15 dm, pubescent in lines above; lvs all cauline, lanceolate or lance-elliptic to linear, serrate or occasionally entire, glabrous or somewhat scabrous above, sessile or tapering to a petiole-like base, sometimes a little clasping, but scarcely auriculate, the main ones 8-15 cm נ3-35 mm, mostly not strongly reticulate, the areolae, if visible, generally irregular and longer than wide; heads ±numerous in an elongate leafy infl, the invol 3-6 mm, its bracts narrow, sharply acute to acutish, glabrous except for the sometimes ciliolate margins, ±strongly imbricate, with elongate, usually appressed green tip; rays 20-40, white or occasionally lavender or blue, 4.5-12 mm; lobes of the disk-cors comprising 30-45% of the limb; 2n=32, 48, 64. Moist low places; N.S. to N.C., w. to N.D. and Tex. (A. paniculatus, a preoccupied name; A. lamarckianus; A. simplex misapplied, the type apparently a garden hybrid of A. laevis and A. lanceolatus var.) Three vars.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.