The Collaborative International Dictionary of English v.0.48:

Athyrium \Athyrium\ n.
   1. 1 a genus temperate and tropical lady ferns; in some
      classifications placed in family Polypodiaceae or in the
      genus Asplenium.

   Syn: genus Athyrium.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Athyrium
    n 1: temperate and tropical lady ferns; in some classifications
         placed in family Polypodiaceae or in the genus Asplenium
         [syn: Athyrium, genus Athyrium]