24. Eupatorium sessilifolium Linnaeus, Sp. Pl. 2: 837. 1753.
Perennials, 50–100+ cm. Stems (from short caudices or rhizomes) single, sparsely branched distally, 5–10+ dm, glabrous or glabrate proximally, puberulent distally (among heads). Leaves usually opposite (distal sometimes alternate); simple, sessile; blades pinnately nerved, lanceolate to oblong, 70–150+ × 10–30 mm (lengths mostly 2–5 times widths), bases truncate to somewhat rounded, margins serrate, apices narrowly acute to acuminate, faces glabrate (scattered, fine hairs), gland-dotted. Heads in corymbiform arrays. Phyllaries 10–15 in 2–3 series, elliptic to oblong, 2–5 × 0.5–1.5 mm, apices rounded to acute (not mucronate), abaxial faces villous to puberulent, gland-dotted. Florets 5; corollas 3–3.5 mm. Cypselae 2–3 mm; pappi of 30–40 bristles 3–4 mm. 2n = 20, 30.
Flowering Jul–Sep. Dry, open, edges of mesic woods; 20–300+ m; Ala., Ark., Conn., Del., Ga., Ill., Ind., Iowa, Kans., Ky., Md., Mass., Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Vt., Va., W.Va., Wis.