mandarin orange vs satsuma

mandarin orange

noun
  • 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). 

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

satsuma

noun
  • A seedless and easy-peeling cultivar of mandarin orange of Japanese origin; Citrus unshiu. 

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