Source : Webster's Revised Unabridged Dictionary (1913)

Acrogen \Ac"ro*gen\, n. [Gr. ? extreme, high + -gen.] Acrogen
\Ac"ro*gen\, n. [Gr. 'a`kros extreme, high + -gen.] (Bot.)
   A plant of the highest class of cryptogams, including the
   ferns, etc. See {Cryptogamia}.

   {The Age of Acrogens} (Geol.), the age of coal plants, or the
      carboniferous era.

Acrogen \Ac"ro*gen\, n. [Gr. ? extreme, high + -gen.] Acrogen
\Ac"ro*gen\, n. [Gr. 'a`kros extreme, high + -gen.] (Bot.)
   A plant of the highest class of cryptogams, including the
   ferns, etc. See {Cryptogamia}.

   {The Age of Acrogens} (Geol.), the age of coal plants, or the
      carboniferous era.

Source : WordNet®

acrogen
     n : any flowerless plant such as a fern (pteridophyte) or moss
         (bryophyte) in which growth occurs only at the tip of the
         main stem