Perennials, 40-100+ cm. Stems (from short rhizomes) single, branched distally, usually glabrous or glabrate, sometimes pilose. Leaves usually opposite (distal sometimes alternate); sessile or subsessile (petioles to 5 mm); blades 3-nerved from bases, lanceolate to lance-linear, 30-50 × 5-13 mm, bases narrowly cuneate, margins serrate, apices acute, faces glabrous adaxially, sparsely pilose abaxially, densely gland-dotted. Heads in corymbiform arrays. Phyllaries 7-10 in 2-3 series, elliptic, 1-4.5 × 0.2-0.8 mm, apices rounded, abaxial faces pilose, gland-dotted. Florets 5; corollas 2.5-3 mm. Cypselae 2.5-2.8 mm; pappi of 30-40 bristles 3.5-4 mm. 2n = 20.

Flowering Aug-Sep. Dry, rolling terrain, clay soils, shade to sun, shortleaf pine and oak woods; 50-200+ m; Ala., Ark., La., Tex.

Eupatorium lancifolium has been combined with E. semiserratum or listed within it as a subspecies; it differs in its habitat as well as in having leaves that are somewhat smaller, typically a dull blue-green (in contrast to yellow-green in E. semiserratum), and 3-nerved from bases of blades.