black haw vs blackhaw

black haw

noun
  • Viburnum prunifolium. 

  • Sideroxylon lanuginosum, also native to Mexico. 

  • Viburnum rufidulum (rusty blackhaw). 

  • Viburnum lentago. 

blackhaw

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