Eupatorium petaloideum Britt.

Eupatorium petaloideum is commonly combined with E. album; it has recently been separated as a distinct variety. V. I. Sullivan (1972) found the two taxa to be distinct chemically and to occupy different habitats. In both, the involucral bracts are white and long-acuminate or mucronate; those of E. petaloideum are almost entirely devoid of any pubescence including glands and those of E. album have both simple and glandular hairs.

Perennials, 30–70 cm. Stems (from short, stout rhizomes) single, branched distally, puber-ulent. Leaves usually opposite (distal sometimes alternate); sessile; blades pinnately nerved, elliptic to ovate, 20–80 × 10–30 mm, bases cuneate, margins serrate to crenate-serrate, apices rounded to acute, faces sparsely villous (abaxial), glabrate (adaxial), little, if at all, gland-dotted. Heads in corymbiform arrays. Phyllaries 9–15 in 2–4 series, linear, 4–10 × 0.6–1 mm, apices (white) acuminate to attenuate, strongly mucronate, abaxial faces glabrous, not gland-dotted. Florets (4–)5; corollas 3–3.5 mm. Cypselae 2.5–3 mm; pappi of 40–50 bristles 3.5–4 mm. 2n = 20.

Eupatorium album Linnaeus var. petaloideum (Britton) R. K. Godfrey ex D. B. Ward