American winterberry vs possumhaw

American winterberry

noun
  • Ilex verticillata, a species of holly native to eastern North America in the United States and southeast Canada, from Newfoundland west to Ontario and Minnesota, and south to Alabama. 

possumhaw

noun
  • American winterberry, Ilex verticillata. 

  • Deciduous Holly, Ilex decidua. 

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