Saint-John's-wort vs St John's wort

Saint-John's-wort

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. 

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