Rhizomatous, sometimes with a short branched caudex as well, 2-12 dm, ±hirsute or hirsute-puberulent especially in the infl and on the lower surfaces of the lvs, varying to essentially glabrous; lvs acute or acuminate, the basal and commonly some of the lower cauline ones petiolate and cordate or often merely subcordate, 4-12 נ2-6 cm, sharply serrate, often deciduous, those above becoming merely abruptly narrowed to the broadly winged petiole, and often less toothed, or the upper sessile and entire; infl open, with relatively few heads (often less than 50, rarely over 100), the branches and peduncles sparsely or scarcely bracteate, the bracts narrow, the peduncles very unequal, generally some over 1 cm; invol 5-8 mm, its slender bracts slightly or moderately imbricate, glabrous except the sometimes ciliolate margins, sharply acute or acuminate, the green tip narrow and elongate; rays 12-25, blue, 8-15 mm; achenes glabrous or nearly so; 2n=48, 72. Woods and clearings; Me. and Que. to N.Y., w. to Minn., S.D., Wyo., Mont., B.C., and Mack. (A. lindleyanus; A. saundersii; A. wilsonii)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.