bindweed vs sweet potato

bindweed

noun
  • black bindweed (Fallopia convolvulus). 

  • true bindweed (Convolvulus). 

  • slender bindweed (Polymeria calycina). 

  • bittersweet nightshade, blue bindweed (Solanum dulcamara). 

  • false bindweed (Calystegia). 

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 bindweed and sweet potato occurred in a corpus of books? (source: Google Ngram Viewer )