clementine vs mandarin orange

clementine

noun
  • A type of small, sweet orange, the result of a cross between a tangerine and Seville orange. 

mandarin orange

noun
  • A small citrus tree (Citrus reticulata) with fruit resembling the orange. 

  • The fruit of this tree, smaller than an orange and oblate. In daily usage, it may include other similar citrus fruits like Citrus unshiu (satsuma or mikan) Citrus tangerina (tangerine). 

How often have the words clementine and mandarin orange occurred in a corpus of books? (source: Google Ngram Viewer )