cowberry vs pyrola

cowberry

noun
  • The berry of this shrub. 

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

pyrola

noun
  • Any of the genus Pyrola of wintergreens. 

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