sweet pepperbush vs white alder

sweet pepperbush

noun
  • Clethra alnifolia, a deciduous flowering shrub of eastern North America. 

white alder

noun
  • American winterberry (Ilex verticillata). 

  • Grey alder (Alnus incana) 

How often have the words sweet pepperbush and white alder occurred in a corpus of books? (source: Google Ngram Viewer )