Rhizomatous; stem 1-7 dm, puberulent in lines decurrent from the lf-bases, at least above; lvs glabrous, or hairy along the midrib beneath, lanceolate to oblong or elliptic, 5-15 cm נ9-40 mm, rather distantly serrulate to occasionally entire, sessile and auriculate-clasping, or the lower tapering and subpetiolate but not enlarged and mostly deciduous; heads few in a corymbiform infl, or solitary; invol glabrous, its bracts scarcely or not at all imbricate, at least some of the outer leafy throughout and surpassing the inner; rays 15-40(-60), blue, 8-17 mm; 2n=32, 48, 64? Moist, exposed or protected places; Nf. to N.B., Me., n. N.H., and apparently n. Vt. (A. tardiflorus, misapplied)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.