bog bilberry vs fraughan

bog bilberry

noun
  • A shrub native of the cool temperate areas of northern hemisphere, Vaccinium uliginosum, and the berry of that shrub. 

fraughan

noun
  • The bilberry or whortleberry (Vaccinium myrtillus). 

How often have the words bog bilberry and fraughan occurred in a corpus of books? (source: Google Ngram Viewer )