Rhizomatous and colonial, 2-10 dm, usually without tufts of radical lvs; stem puberulent at least in the infl, not glandular; lvs rather thin, sharply serrate with usually mucronate teeth, glabrous or with some long, mostly appressed hairs, especially along the main veins beneath; lower lvs ovate (often narrowly so), with cordate base, conspicuously acuminate, 4-20 נ2-10 cm, petiolate, the lowest often smaller than those above and commonly deciduous, the middle and upper ones progressively less cordate, less petiolate, and ±reduced; infl corymbiform, occasionally becoming elongate, its bracts few and often broad; invol 5-10 mm, its bracts firm, well imbricate, rounded to acute, very shortly green-tipped, otherwise mostly whitish, the outer 0.7-1.5 mm wide (or a little wider in var. chlorolepis) and seldom more than 2.5 times as long; rays 5-16(-20), white, or in var. chlorolepis sometimes lilac-tinged; 2n=18, 36. Woods; n. N.H. and sw. Que. (just n. of Lake Champlain), w. to the Niagara peninsula of s. Ont., s. to D.C. and s. O., and in the mt. region to n. Ga. and e. Ala. (A. carmesinus; A. castaneus; A. excavatus; A. stilletiformis; A. tenebrosus) The widespread var. divaricatus, diploid, with relatively small heads, the invol 5-8 mm, the rays 5-10(-12), 5-15 mm, gives way at upper elev. in the Blue Ridge of sw. Va., N.C., Tenn., and n. Ga. to the var. chlorolepis (Burgess) Ahles, tetraploid, with relatively large heads, the invol 7-10 mm, its bracts avg broader, and with not so pale chartaceous part, the inner ones often purplish distally, the rays (10-)12-16(-20), 10-20 mm. (A. chlorolepis)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.