galangal vs ginger root

galangal

noun
  • Any of several east Asian plants of genera Alpinia and Kaempferia in the ginger family, used as a spice, but principally Alpinia galanga. 

ginger root

noun
  • Ginger, the underground stem, or rhizome, of the plant Zingiber officinale. 

How often have the words galangal and ginger root occurred in a corpus of books? (source: Google Ngram Viewer )