black radish vs radish

black radish

noun
  • A root vegetable of the family Brassicaceae cultivated for its edible root that has a tough black or dull brown skin and white flesh, Raphanus sativus var. niger 

radish

noun
  • A plant of the Brassicaceae family, Raphanus sativus or Raphanus raphanistrum subsp. sativus, having an edible root. 

  • With a distinguishing word: some other plant of the Raphanus genus or Brassicaceae family. 

  • The root of this plant used as food. Some varieties are pungent and usually eaten raw in salads, etc., while others have a milder taste and are cooked. 

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