Eupatorium altissimum (tall thoroughwort) is a perennial plant whose native range includes much of the eastern and central United States and Canada (Ontario south to Nebraska, eastern Texas, the Florida Panhandle, and Massachusetts. It almost always grows on limestone soils, as does Brickellia eupatorioides, with which it is often confused. It can hybridize with Eupatorium serotinum. Eupatorium altissimum is part of Eupatorium even when that genus is defined narrowly to include about 40 species of mostly white-flowered plants of North America, Asia, and Europe.