cow's lungwort vs great mullein

cow's lungwort

noun
  • mullein (Verbascum thapsus) 

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 cow's lungwort and great mullein occurred in a corpus of books? (source: Google Ngram Viewer )