lemon balm vs mountain mint

lemon balm

noun
  • A perennial herb, Melissa officinalis, of southern Europe; used as a flavouring in ice cream etc. 

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. 

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