cowberry vs mountain cranberry

cowberry

noun
  • The berry of this shrub. 

  • A shrub native to the cool temperate areas of the Northern Hemisphere (Vaccinium vitis-idaea). 

mountain cranberry

noun
  • The cowberry, Vaccinium vitis-idaea 

  • The mountain bearberry, Arctostaphylos alpina 

How often have the words cowberry and mountain cranberry occurred in a corpus of books? (source: Google Ngram Viewer )