Ageratina altissima

Perennials, (30-)50-80(-120) cm (bases usually fibrous-rooted crowns, sometimes rhizomatous). Stems ascending to erect, sometimes semiscandent, puberulent (hairs minute, crisped). Leaves opposite; petioles (5-)10-30(-50) mm; blades usually deltate-ovate to ovate or broadly lanceolate, sometimes ovate-lanceolate, 4-11(-13) × 2.5-8(-9) cm, bases usually rounded to truncate or obtuse, sometimes cordate, margins coarsely and doubly incised-serrate, apices usually acuminate. Heads clustered. Peduncles 1-5 mm, puberulent. Involucres 4-5 mm. Phyllaries: apices acute, abaxial faces glabrous or sparsely and finely villous. Corollas white, lobes sparsely short-villous. Cypselae glabrous.

Stems 1-3, 3-15 dm, glabrous below the infl and sometimes glaucous, or shortly and loosely hairy; lvs opposite, narrowly to broadly ovate or even subcordate, rather thin, glabrous or hairy especially on the main veins beneath, serrate, usually sharply and coarsely so, mostly acuminate, the larger ones mostly 6-18 נ3-12 cm (or smaller in depauperate plants), 1.5-5 times as long as the well developed petiole; infl flat-topped or more rounded, invol 3-5 mm, glabrous or short-hairy, its principal bracts subequal and subbiseriate, acuminate to obtuse; fls mostly (9-)12-25 per head, cor bright white, mostly 3-4 mm, its lobes often short-hairy; achenes generally glabrous; 2n=34. Woods; N.S. to Sask., s. to Ga. and Tex. July-Oct. (E. urticaefolium) Poisonous. Our plants are var. rugosum. Var. roanense (Small) Fernald, with larger heads (invol to 7 mm, fls to 34), occurs on the highest mts. of Tenn. and N.C.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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