Spanish chestnut vs horse chestnut

Spanish chestnut

noun
  • Castanea sativa, a deciduous tree with edible deep brown nutlike fruits. The fruits have a little white, fluffy tail. 

  • The fruit of this tree. 

horse chestnut

noun
  • Any of several tree species of genus Aesculus, especially Aesculus hippocastanum, common in temperate northern hemisphere. 

  • The large nutlike seed of these trees. 

How often have the words Spanish chestnut and horse chestnut occurred in a corpus of books? (source: Google Ngram Viewer )