Lanceleaf Thoroughwort

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.

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.

Eupatorium parviflorum Elliott [not Aublet] var. lancifolium Torrey & A. Gray, Fl. N. Amer. 2: 85. 1841; E. semiserratum de Candolle var. lancifolium (Torrey & A. Gray) A. Gray

Eupatorium lancifolium, commonly called lanceleaf thoroughwort, is a North American herbaceous perennial plant in the family Asteraceae native to the south-central United States (Mississippi, Alabama, Arkansas, Louisiana and Texas).

It is related to Eupatorium semiserratum and has sometimes been considered to be part of that species, but can be distinguished by the size and color of the leaves and because it grows in wetter areas.