sweet potato vs taro

sweet potato

noun
  • The tuber of this plant cooked as a vegetable. 

  • An ocarina. 

  • A tropical perennial American vine, Ipomoea batatas, having a fleshy tuber. 

taro

noun
  • Colocasia esculenta, raised as a food primarily for its corm, which distantly resembles potato. 

  • Any of several other species with similar corms and growth habit in Colocasia, Alocasia etc. 

  • Food from a taro plant. 

How often have the words sweet potato and taro occurred in a corpus of books? (source: Google Ngram Viewer )