The Collaborative International Dictionary of English v.0.48:

Hamamelidanthum \Hamamelidanthum\ n.
   A genus of fossil plants of the Oligocene having flowers
   resembling those of the witch hazel; found in Baltic region.

   Syn: genus Hamamelidanthum.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Hamamelidanthum
    n 1: genus of fossil plants of the Oligocene having flowers
         resembling those of the witch hazel; found in Baltic region
         [syn: Hamamelidanthum, genus Hamamelidanthum]