The Collaborative International Dictionary of English v.0.48:

Geastrum \Geastrum\ prop. n.
   The type genus of the Geastraceae, consisting of fungi
   whose outer peridium when dry splits into starlike segments.

   Syn: genus Geastrum.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Geastrum
    n 1: type genus of Geastraceae; fungi whose outer peridium when
         dry splits into starlike segments [syn: Geastrum, genus
         Geastrum]