Perennials, 30-100+ cm. Stems (from short rhizomes) single, sparsely branched distally, densely puberulent to pilose throughout. Leaves usually opposite (distal sometimes alternate); simple, sessile or subsessile; blades ± 3-nerved (distal to bases), elliptic, lanceolate, or lance-ovate, 30-90 × 20-45 mm (lengths mostly 2-2.5 times widths), bases rounded to rounded-cuneate, margins unevenly serrate, apices acute to attenuate, faces puberulent, gland-dotted. Heads in corymbiform arrays. Phyllaries 7-10 in 2-3 series, oblong to lance-oblong, 2-7 × 1-1.5 mm, apices (sometimes whitish) acuminate to acute, mucronate, abaxial faces puberulent, gland-dotted. Florets 5; corollas 3.5-4 mm. Cypselae 3-4 mm; pappi of 30-50 bristles 4-5 mm. 2n = 20, 30, 40. Flowering Jul-Sep. Moist, low ground, margins of ponds, sandy soils, savannas, ditches; 20-100+ m; Ala., Conn., Del., Fla., Ga., Ky., La., Md., Mass., Miss., N.J., N.Y., N.C., Pa., R.I., S.C., Tenn., Va., W.Va. Eupatorium pilosum has been most commonly treated as a variety of E. rotundifolium; it is distinct morphologically by its leaves, which are narrower and 3-nerved distal to bases, rather than 3-nerved from bases. Distal leaves of E. pilosum tend to differ from the proximal by being alternate with entire margins.