citronella vs lemongrass

citronella

noun
  • A tropical Asian grass, Cymbopogon nardus, that has citrus-scented leaves. 

  • An essential oil obtained from this plant, often used as an insect repellent. 

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 citronella and lemongrass occurred in a corpus of books? (source: Google Ngram Viewer )