Rubus parviflorus vs salmonberry

Rubus parviflorus

salmonberry

noun
  • A bush, Rubus spectabilis, found on the Pacific coast of North America. 

  • The fruit from this bush, similar in appearance and texture to the blackberry and raspberry. 

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