great mullein vs roseroot

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. 

roseroot

noun
  • Rhodiola rosea, a perennial crassulaceous plant with many claimed health benefits that grows in cold regions. 

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