The Collaborative International Dictionary of English v.0.48:

Horneophyton \Horneophyton\ n.
   A genus of Devonian fossil plants considered one of the
   earliest forms of vascular land plants; it is similar to
   genus Rhynia but smaller.

   Syn: genus Horneophyton.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Horneophyton
    n 1: Devonian fossil plant considered one of the earliest forms
         of vascular land plants; similar to genus Rhynia but
         smaller [syn: Horneophyton, genus Horneophyton]