Michigan holly vs black alder

Michigan holly

noun
  • American winterberry, Ilex verticillata. 

black alder

noun
  • American winterberry, Ilex verticillata. 

  • Wood or other product of the tree. 

  • A tree (Alnus glutinosa), of many practical uses, growing in moist conditions in Europe. 

How often have the words Michigan holly and black alder occurred in a corpus of books? (source: Google Ngram Viewer )