St John's wort vs ground ivy

St John's wort

noun
  • The plant prepared as a medication. 

  • Any of several plants, of the genus Hypericum, especially Hypericum perforatum, that have yellow flowers and traditionally ward off evil. 

ground ivy

noun
  • Glechoma hederacea, an aromatic, perennial, evergreen creeper of the mint family Lamiaceae. 

How often have the words St John's wort and ground ivy occurred in a corpus of books? (source: Google Ngram Viewer )