Source : Webster's Revised Unabridged Dictionary (1913)

Usnic \Us"nic\, a. (Chem.)
   Pertaining to, or designating, a complex acid obtained, as a
   yellow crystalline substance, from certain genera of lichens
   ({Usnea}, {Parmelia}, etc.).

Source : WordNet®

Parmelia
     n : type genus of the Parmeliaceae; a large genus of chiefly
         alpine foliaceous lichens [syn: {genus Parmelia}]