summersweet vs sweet pepperbush

summersweet

noun

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

sweet pepperbush

noun

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

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