Tulip Poplar, a native species, has been added to the USWildflowers database (11/26/2010.)  Scientific name is Liriodendron tulipifera.  It is also known by the common names Yellow Poplar, Tuliptree, and Tulip Magnolia.  Photo below was taken The Pocket at Pigeon Mountain in Walker County, GA on May 13, 2008. 

Tulip Poplar, Yellow Poplar, Tuliptree, Tulip Magnolia - Liriodendron tulipifera