bog bilberry vs whortleberry

bog bilberry

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

whortleberry

noun
  • A berry of one of these shrubs. 

  • Vaccinium vitis-idaea (lingonberry or red whortleberry); 

  • Vaccinium myrtillus (bilberry or blue whortleberry); 

  • Vaccinium uliginosum (bog whortleberry or bilberry). 

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