Late Purple Aster, a native species, has been added to the USWildflowers database (10/22/2010.)  Scientific name is Symphyotrichum patens. Photo below was taken in Blount County, TN on the banks of the Tellico Reservoir of the Little Tennessee River on Oct 16, 2010. 

Late Purple Aster, Spreading Aster – Symphyotrichum patens