The Collaborative International Dictionary of English v.0.48:

gall-of-the-earth \gall-of-the-earth\ n.
   A common perennial herb (Nabalus serpentarius) widely
   distributed in southern and eastern U. S., having drooping
   clusters of pinkish flowers and thick basal leaves suggesting
   a lion's foot in shape; sometimes placed in the genus
   Prenanthes.

   Syn: lion's foot, gall of the earth, Nabalus serpentarius,
        Prenanthes serpentaria.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Nabalus serpentarius
    n 1: common perennial herb widely distributed in the southern
         and eastern United States having drooping clusters of
         pinkish flowers and thick basal leaves suggesting a lion's
         foot in shape; sometimes placed in genus Prenanthes [syn:
         lion's foot, gall of the earth, Nabalus serpentarius,
         Prenanthes serpentaria]