collard greens vs lettuce

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. 

lettuce

noun
  • An edible plant, Lactuca sativa and its close relatives, having a head of green and/or purple leaves. 

  • long hair, as worn by an exemplar of bro culture 

  • The leaves of the lettuce plant, eaten as a vegetable; as a dish often mixed with other ingredients, dressing etc. 

  • United States paper currency; dollars. 

  • A strong yellow-green colour, like that of lettuce (also called lettuce green). 

  • weed or marijuana 

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