White snakeroot

Ageratina altissima, the white snakeroot or white sanicle (formerly Eupatorium rugosum), is an erect perennial herb in the family Asteraceae native to eastern and central North America, occurring from southern Canada south to the Gulf states and west to the Great Plains. It grows in moist deciduous woodland, shaded ravines, woodland edges, and shaded fence rows. The plant arises from a fibrous-rooted crown and produces clustered erect stems 30-150 cm tall that are smooth, slender, and freely branched in the upper portion. Leaves are opposite, long-petioled, broadly ovate to ovate-cordate, 6-15 cm long, with coarsely serrate margins, an acuminate apex, and a rounded to subcordate base; the surface is sparsely hairy to glabrate. The inflorescence is a flat-topped compound corymb of numerous small heads, each 3-5 mm across with 12-25 brilliant white tubular disc florets and no ray florets, the involucre cylindrical with a single row of narrow green bracts. Flowering occurs from midsummer to autumn. The achenes are five-angled, black, and bear a single row of fine white pappus bristles. The entire plant contains the toxin tremetol and was the cause of historical "milk sickness" outbreaks when cattle grazed the foliage.