Oakleaf Hydrangea, a native species, has been added to the USWildflowers database (11/27/2010.)  Scientific name is Hydrangea quercifolia.  It is the state wildflower of Alabama.  Photo below was taken Reflection Riding in Hamilton County, TN on Aug 28, 2010. 

Oakleaf Hydrangea – Hydrangea quercifolia