gray box bush vs pignut

gray box bush

pignut

noun
  • The edible tuber of Conopodium majus, native to western Europe. 

  • Any of various types of hickory or their fruits; a hognut. 

  • Simmondsia chinensis, jojoba. 

How often have the words gray box bush and pignut occurred in a corpus of books? (source: Google Ngram Viewer )