Whorled Horsebalm, a native species, has been added to the USWildflowers database (05/05/2011.)  Scientific name is Collinsonia verticillata.  Photo below was taken on Lookout Mountain in Hamilton County, Tennessee in the Chattanooga and Chickamauga National Military Park on April 25, 2011.

Whorled Horsebalm, Early Stoneroot – Collinsonia verticillata