Perennials, 40-100+ cm. Stems (from short caudices or stout rhizomes) single, sparsely branched distally, puberulent throughout (more densely distally and among heads). Leaves usually opposite (distal sometimes alternate, ascending to vertical); sessile; blades pinnately nerved, lance-oblong to linear-oblong, 20-60 × 4-10(-15) mm, bases rounded to cuneate (not connate-perfoliate), margins entire or serrate, apices acute, faces villous (abaxial), scabrous (adaxial), gland-dotted. Heads in corymbiform arrays. Phyllaries 8-10 in 2-3 series, narrowly elliptic, 2.5-8 × 0.8-1.2 mm, acuminate to attenuate, mucronate, abaxial faces puberulent, gland-dotted. Florets 5; corollas 3-3.5 mm. Cypselae 2-3 mm; pappi of 30-40 bristles 4.5-5 mm. Eupatorium leucolepis is distinct morphologically by its acuminate to attenuate phyllaries, linear and usually plicate leaves, and phyllotaxy that is almost always strictly opposite to the arrays, with well-separated nodes. Eupatorium leucolepis has recently been shown to include two distinct species, an unnamed diploid that is endemic to Carolina Bay habitats and a series of relatively widespread and mostly polyploid, apomictic populations that include the type. It was recognized after preparation of this treatment that E. novaeangliae (E. leucolepis var. novaeangliae) was derived from hybridization between the unnamed diploid and E. perfoliatum, and is here recognized as a distinct species; it is not directly related genetically to E. leucolepis and thus is not appropriately classified as a variety of it.
Stem 4-10 dm from a crown or short, stout rhizome, hirtellous or puberulent to sometimes merely strigose; lvs opposite, lance-oblong to linear-oblong or oblanceolate, 3-8 cm נ3-10(-13) mm, toothed or entire, sessile, glandular-punctate; invol 5-7 mm, its bracts imbricate, narrow, tapering to a long-acuminate or mucronately subattenuate point, conspicuously villous-puberulent and often also atomiferous-glandular, their scarious margins mostly inconspicuous; fls 5, the cor white, 3-4 mm; 2n=20, 30, 40. Pine-barrens, wet meadows, and margins of ponds, especially in sandy soil; Mass. to Fla. and La., on the coastal plain or near the coast. July-Oct. Var. leucolepis, from N.Y. s., has bluntly few-toothed to entire lvs, often folded along the midrib. Var. novae-angliae Fernald, local in Mass. and R.I., has sharply toothed, flat lvs, often with slightly longer pubescence than in var. leucolepis.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.