Joe Pye Weed floret

The attractive and distinctive pale purple florets of Spotted Joe-Pye Weed, Eupatoriadelphus maculatus (sometimes called spotted trumpetweed), a native perennial in the aster family, appear in mid-to-late summer.
 
For more about Spotted Joe-Pye Weed and native plants for the Midwest, especially those that do well in shade/moist areas, see the "book" on this website, Gardening with Native Plants in Shady Evanston.