Black Cohosh, a native species, has been added to the USWildflowers database (05/28/2011.)  Scientific name is Cimicifuga racemosa.   It is also known by the common names Black Bugbane, Black Baneberry, Black Snakeroot, and Fairy Candle.  Photo below was taken at Reflection Riding in Hamilton County, TN on May 27, 2011. 

Black Cohosh, Black Bugbane - Cimicifuga racemosa