Perennials, 60-100+ cm. Stems (from short caudices) single or multiple, sparsely branched distally, puberulent throughout. Leaves usually opposite (distal sometimes alternate, spreading or horizontal); sessile; blades pinnately nerved, elliptic or lance-ovate to narrowly ovate, 50-100 × 15-40 mm, bases rounded to cuneate (not connate-perfoliate), margins serrate, apices acute, faces puberulent or villous, gland-dotted. Heads in corymbiform arrays. Phyllaries 7-10 in 2-3 series, lanceolate (tapering at tips), 2-6 × 1-1.5 mm, apices acute, not mucronate, abaxial faces puberulent, gland-dotted. Florets (4-)5; corollas 3-3.5 mm. Cypselae 2-3 mm; pappi of 20-50 bristles 3.5-4.5 mm. 2n = 30, 40. Flowering Jul-Sep. Dry, open, disturbed sites, edges of deciduous woods; 20-300+ m; Ky., Md., N.J., N.C., Ohio, Va., W.Va. Eupatorium godfreyanum is an apomictic polyploid derivative that includes genomes from E. rotundifolium and E. sessilifolium. Although it is relatively narrow in distribution, it is known to occur in localities where both progenitor species are absent and it seems to be persistent where it occurs. Eupatorium vaseyi Porter has been misapplied to E. godfreyanum.
Much like no. 17 [Eupatorium sessilifolium L.], but more hairy, the stem loosely puberulent down to the middle or even to the base, the leaves also somewhat puberulent, especially beneath; lvs mostly 5-11 נ1.5-4.5 cm, 2-3(-3.5) times as long as wide, the base often more cuneate and not so broadly rounded as in no. 17, the venation strictly pinnate; 2n=30, 40. Woods and disturbed, open sites, usually in less acid soils than no. 17; N.J., Md., Va., and W.Va. to N.C. and Tenn. July-Sept. (E. vaseyi, misapplied) Possibly originating through hybridization of nos. 17 and 19 [Eupatorium rotundifolium L.], but now widespread and stable.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.