Stem generally glabrous or nearly so, sometimes spreading-hairy toward the base; most of the lvs, except for a few upper ones, generally ±evidently wing-petiolate, the lower surface glabrous or short-hairy, seldom any of the hairs as much as 1 mm; head with mostly 16-35 (commonly ca 21 or 34) rays; invol bracts glabrous except for the ciliate margins; widespread, mainly to the w. or n. of var. connatum.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.