[1] : The Collaborative International Dictionary of English v.0.48

acrogen \ac"rogen\, n. gr. 'a`kros extreme, high + -gen.
   bot.
   a plant of the highest class of cryptogams, including the
   ferns, etc. see cryptogamia.
   1913 webster

   the age of acrogens geol., the age of coal plants, or the
      carboniferous era.
      1913 webster
see also:
cryptogamia the age of acrogens 

[2] : WordNet (r) 2.0

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

Acrogen >> A Words
Acrogen, definition of term: Acrogen
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