Eupatorium (you pah TORE ee um) is the botanical name for Joe Pye weed. Another common name is boneset, which suggests that it was once used medicinally for orthopedic purposes.
There are about 40 species in the Eupatorium genus and most are native American wildflowers. Established plants can spread to form three-to-four-foot clumps, and many types grow to seven feet tall. Fistulosum, known as the hollow Joe Pye weed, has hollow purple-colored stems and big clusters of pinky-purple flowers in midsummer and can reach ten feet in zones 3 to 8.
The species known as rugosum, with the common name of white snakeroot, has clusters of white flowers from midsummer to fall. There's also a variety known as Eupatorium ‘chocolate' with purple/ brown foliage, and it, like the white-flowered rugosum, is hardy in zones 3 to 7.
All species like sun and self-sow and can be divided in early summer.
Most gardens don't have room for such big plants, so if you are short of space, try ‘Baby Joe', which is a miniature eupatorium with dark red/purple stems topped with large mauve blossom clusters in the fall. The butterflies adore ‘Baby Joe' and you will too!