The Collaborative International Dictionary of English v.0.48:

clammyweed \clammyweed\ n.
   strong-scented herb (Polanisia graveolens) common in the
   southern U. S. covered with intermixed gland and hairs.

   Syn: Polanisia graveolens, Polanisia dodecandra.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

clammyweed
    n 1: strong-scented herb common in southern United States
         covered with intermixed gland and hairs [syn: clammyweed,
         Polanisia graveolens, Polanisia dodecandra]