redroot vs tormentil

redroot

noun
  • Any of several plants with red roots, such as the New Jersey tea (Ceanothus americanus), the gromwell (Lithospermum arvense), the bloodroot (Sanguinaria canadensis), and Lachnanthes caroliniana (syn. Lachnanthes tinctoria). 

tormentil

noun
  • A low-growing herb (Potentilla erecta, syn. Potentilla tormentilla). 

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