Source : Webster's Revised Unabridged Dictionary (1913)

Subgenus \Sub*ge"nus\, n.; pl. {Subgenera}. (Biol.)
   A subdivision of a genus, comprising one or more species
   which differ from other species of the genus in some
   important character or characters; as, the azaleas now
   constitute a subgenus of Rhododendron.

Source : WordNet®

subgenus
     n : (biology) taxonomic group between a genus and a species
     [also: {subgenera} (pl)]