Beta vulgaris rubra vs beetroot

Beta vulgaris rubra

beetroot

verb
  • To turn a bright red or purple colour. 

noun
  • A normally deep-red-coloured root vegetable usually cooked or pickled before eating; Synonym of beet. 

  • The edible part of the root of a beet plant, raw or prepared. 

How often have the words Beta vulgaris rubra and beetroot occurred in a corpus of books? (source: Google Ngram Viewer )