bog bilberry vs whortle bush

bog bilberry

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

whortle bush

noun
  • Any of several shrubs belonging to the genus Vaccinium, bearing fruit known as whortleberries. 

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