boniato vs tropical sweet potato

boniato

noun
  • A Cuban type of sweet potato with light-colored flesh that is drier and less sweet than the varieties typical in the US (Ipomoea batatas). 

tropical sweet potato

noun
  • Synonym of white sweet potato 

  • Synonym of name (yam) 

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