common bean vs cowpea

common bean

noun
  • A bean of such a plant, varying in size, shape and especially color. 

  • An herbaceous annual plant (Phaseolus vulgaris), grown for its edible bean. 

cowpea

noun
  • Any of the plants in the species Vigna unguiculata, including the black-eyed pea. 

How often have the words common bean and cowpea occurred in a corpus of books? (source: Google Ngram Viewer )