[Ageratina ageratoides (L. fil.) Spach, moreEupatorium aboriginum E. Greene, Eupatorium ageratoides var. angustatum A. Gray, Eupatorium rugosum H.B. & K., Eupatorium urticifolium var. villicaule Fern.]
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.
Frequent to common in most of the dry and moist woods of the state. It is more common in beech and sugar maple and black and white oak woods. This plant is poisonous to grazing animals and if it is eaten in a sufficient quantity it proves fatal. A symptom of having eaten too much of this weed is a trembling of the animal and because of this characteristic, the disease has been called "trembles." The plant is frequently eaten by sheep and by cattle when the pasturage becomes scarce, and many of those animals are killed in Indiana each year by this weed. When it is eaten by milk cows, the poisonous principle (a barium salt) is communicated to the milk; such milk, when consumed by people, has the same effect as the plant has upon stock. The pioneers called it "milk sickness," and many of them died from drinking too much of the affected milk. A pioneer informed me that a family of four in my own county died from this cause. Indiana specimens show some variation in leaf form. All of my specimens are generally densely short-pubescent in the inflorescence and on the upper half of the stem, and in a few plants the stem is villous. (See Rhodora 10: 87. 1908.) The leaves of all of my specimens are abruptly cuneate at the petiole except in my Lake and Warren County specimens in which they are slightly cordate at the base.
Indiana Coefficient of Conservatism: C = 2
Wetland Indicator Status: FACU
Diagnostic Traits: Leaves opposite, petiolate, deltate; ray flowers absent; disk flowers white, 3-4 mm; pappus of numerous capillary bristles.
Indiana populations belong to the widespread var. altissima.