furze vs thistle sage

furze

noun
  • A thorny evergreen shrub, with yellow flowers, Ulex gen. et spp., of which Ulex europaeus is particularly common upon the plains and hills of Great Britain and Ireland. 

thistle sage

noun
  • A North American herb, Salvia carduacea, the seeds of which were once a staple food similar to chia 

How often have the words furze and thistle sage occurred in a corpus of books? (source: Google Ngram Viewer )