citrus fruit vs mikan

citrus fruit

noun
  • Any of the fruits in the common genus Citrus of flowering plants in the family Rutaceae. 

mikan

noun
  • An orange seedless citrus fruit Citrus unshiu, originating from Japan, about the size of a tangerine. 

How often have the words citrus fruit and mikan occurred in a corpus of books? (source: Google Ngram Viewer )