Roman camomile vs camomile

Roman camomile

noun
  • Chamaemelum nobile, one of the two species of plants most commonly known as camomile. 

camomile

noun
  • Any of several other similar plants. (See below) 

  • Matricaria recutita (formerly known as Matricaria chamomilla), German chamomile or Hungarian chamomile, with fragrant flowers used for tea, and as an herbal remedy. 

  • Chamaemelum nobile (formerly Anthemis nobilis), English chamomile or Roman chamomile, a ground cover with fragrant foliage. 

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