Wordnet 3.0
NOUN (1)
1. 
 whisk ferns; 
 comprising the family Psilotaceae or Psilotatae: vascular plants with no roots, partial if any leaf differentiation, and rudimentary spore sacs; 
[syn: Psilopsida, class Psilopsida, Psilotatae, class Psilotatae]
WordNet (r) 3.0 (2006):
class Psilotatae
    n 1: whisk ferns; comprising the family Psilotaceae or
         Psilotatae: vascular plants with no roots, partial if any
         leaf differentiation, and rudimentary spore sacs [syn:
         Psilopsida, class Psilopsida, Psilotatae, class
         Psilotatae]