Spotted Joe-Pye Weed, Eupatoriadelphus maculatus, sometimes called spotted trumpetweed, is a hardy and fast-growing long-stemmed perennial in the aster family, indigenous to the eastern U.S. from the Great Plains to New England. In Illinois, it's found naturally in counties mainly in the northern half of the state. Spotted Joe-Pye Weed is more shade-tolerant and moisture-loving than its cousin, Sweet Joe-Pye Weed (Eupatoriadelphus purpureum), and does well in woodlands-type settings, even with occasional temporary inundation.
Spotted Joe-Pye is recognizable by its purple stems (sometimes covered with downy fibers). It reappears in the spring as small purple shoots creeping along the ground, then grows rapidly during the season to a stemmy, gently arching plant of between 3' and 6' tall depending on soil conditions (the specimen shown above has to compete with maple roots for water and nutrients). In late summer, flat-headed pinkish to pale-purple bloom clusters (seen above) appear. The plant shown below is an example of its rapid growth: it grew from 1" shoots to the 5 feet tall pictured in about three months. Reportedly, it will naturalize and multiply given the opportunity.