mayweed vs primula

mayweed

noun
  • Plants of the genera Matricaria and Tripleurospermum. 

  • corn chamomile, field chamomile, Anthemis arvensis. 

  • A mayflower. 

  • stinking chamomile, Anthemis cotula. 

primula

noun
  • Any plant of the genus Primula; the primroses. 

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