colewort vs collard greens

colewort

noun
  • A plant of the genus Brassica; now specifically, a Brassica plant without a head used for food, such as kale. 

collard greens

noun
  • A form of Brassica oleracea, sometimes called Brassica oleracea var. acephala or Brassica oleracea var. viridis, similar to kale, that is a popular food in the rural southern United States. 

How often have the words colewort and collard greens occurred in a corpus of books? (source: Google Ngram Viewer )