cassava vs sweet potato

cassava

noun
  • Tapioca, a starchy pulp made with manioc roots. 

  • Manioc (Manihot esculenta), a tropical plant which is the source of tapioca. 

sweet potato

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

  • The tuber of this plant cooked as a vegetable. 

  • An ocarina. 

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