lemon balm vs lemongrass

lemon balm

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

lemongrass

noun
  • One of various species of grass of the genus Cymbopogon, especially Cymbopogon citratus, which have a lemon-like taste and aroma, and are used in cooking, for tea, and for fragrance. 

  • Sourgrass, Oxalis pes-caprae. 

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