Asteraceae : Eupatorium perfoliatum
Eupatorium perfoliatum is a perennial herb arising from a rhizome, with stems, covered with hairs, that grow from 40 to 150 cm tall. The simple, opposite leaves clasp the stems. The blades are broad at the base and taper to a point at the tip, 7-20 cm long and up to 4 cm wide, with toothed margins and hairy lower sides. The inflorescence is made up of flat-topped clusters of heads. Each head has a 4-6 mm involucre of overlapping bracts in several series. There are 9-23 white disk flowers that produce 5-sided achenes that have a bristly pappus. Boneset blooms in August and September in damp prairies and bogs in the eastern edge of South Dakota.