Ageratina altissima (L.) R. M. King & H. Rob.
Family: Asteraceae
White Snakeroot
Ageratina altissima image
John Hilty  

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.

Ageratina altissima image
John Hilty  
Ageratina altissima image
John Hilty  
Ageratina altissima image
Gretchen Jones @ http://pollen.usda.gov/index.htm  
Ageratina altissima image
Taken from Nesom, Guy L. "Ageratina" in Flora of North America, Vol. 21, p. 549. Oxford University P  
Ageratina altissima image
G.A. Cooper @ USDA-NRCS PLANTS Database  
Ageratina altissima image
G.A. Cooper @ USDA-NRCS PLANTS Database