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