common mullein vs great mullein

common mullein

noun
  • Verbascum thapsus; great mullein 

great mullein

noun
  • A common herb of Europe and neighboring Africa and Asia, but widely naturalized elsewhere, Verbascum thapsus, having a flannel-like texture from course plant hairs and a tall, straight flower stalk. 

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