Northwest Naturalist

Polypodium calirhiza “California Licorice Fern” Polypodiaceae

Mt. Tamalpais State Park, Marin County, CA
December 29, 2015
Robert Niese

P. calirhiza is a hybrid of the California Polypody (P. californicum) and Licorice Fern (P. glycyrrhiza) that was formally recognized as a separate species in 1991. These hybrids persist as a unique species because of their doubled chromosome number (2n=148 instead of 74) which produces sterile back-crosses (2n=111). Speciation by this sort of genome duplication event is surprisingly common among plants. In coastal California, all three species often occur side-by-side, but P. californicum does not grow on other plants (as seen here) and P. glycyrrhiza has rhizomes with a pleasant, sweet licorice flavor (P. calirhiza has a disappointingly sweet, even acrid taste). This hybrid polypody occurs throughout California, north to Oregon, west of the Cascades and Sierras.