Stems 6-20 dm, glabrous or nearly so below the infl, slightly glaucous, usually purple only or chiefly at the nodes, otherwise greenish, usually solid, the pith remaining intact or ultimately developing a slender central cavity; lvs mostly in 3's or 4's, lanceolate to ovate or elliptic, 8-30 נ2.5-15 cm, gradually or sometimes rather abruptly narrowed to the short petiole, pinnately veined, usually sharply toothed, the lower surface glabrous or sparsely and inconspicuously short-hairy; infl convex; invol imbricate, 6.5-9 mm, its bracts well imbricate, commonly 3-nerved, obtuse or acutish; fls 4-7 per head, generally very pale pinkish or purplish, but variable; 2n=20, 40. Thickets and open woods, often in drier habitats than related spp.; s. N.H. to Va. and in the mts. to Ga., w. to Wis., Io., Okla., and w. Fla. July-Sept. (E. trifoliatum.) Plants from our western border, as in Minn., Io., and Mo., have the lvs more evidently short-hairy across the surface beneath, and have been distinguished as var. holzingeri (Rydb.) E. E. Lamont.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.