mountain mint vs mountain-mint

mountain mint

noun
  • Any of several plants in the genus Monardella, native to western North America 

  • A European herb, Clinopodium nepeta, sometimes used as a seasoning. 

  • Any plant of the genus Pycnanthemum in the mint family. 

mountain-mint

How often have the words mountain mint and mountain-mint occurred in a corpus of books? (source: Google Ngram Viewer )