4. Ageratina aromatica (Linnaeus) Spach, Hist. Nat. Vég. 10: 286. 1841.
Small-leaved white snakeroot
Eupatorium aromaticum Linnaeus, Sp. Pl. 2: 839. 1753; E. latidens Small
Perennials, 30–80(–100) cm. Stems erect, villous-puberulent. Leaves opposite; petioles 1–8(–12) mm; blades narrowly to broadly deltate to nearly ovate or lanceolate, 2–7(–9) × 1.5–4 cm, (usually subcoriaceous) bases rounded or truncate to barely cuneate or subcordate, margins usually crenate, sometimes crenate-serrate to dentate or subentire, apices acute to obtuse, faces minutely pilose. Heads clustered. Peduncles 2–9 mm, densely and closely puberulent. Involucres 3.5–5 mm. Phyllaries: apices acute, abaxial faces puberulent to villous-puberulent. Corollas white, lobes sparsely villous. Cypselae usually glabrous or sparsely puberulent (near apices), rarely hirtellous on angles. 2n = 34.
Flowering late Aug–Oct(–Nov). Sandy soils, burned pinelands, turkey oak sand ridges, pine-oak and oak-hickory upland woods, old fields, roadsides, fencerows, moist sites; 100–900 m; Ala., Conn., Del., Fla., Ky., La., Md., Mass., Miss., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Va., W.Va.
Intergrades (probable hybrids) between Ageratina aromatica and A. altissima were identified by A. F. Clewell and J. W. Wooten (1971) over a broad area of their sympatry. They also found intergrades between A. aromatica and A. jucunda where their ranges meet.