Horkelia is a genus of herbaceous perennial flowering plants in the rose family, Rosaceae, placed within the order Rosales. The genus was described by Adelbert von Chamisso and Diederich Franz Leonhard von Schlechtendal and published in Linnaea in 1827. Horkelia is closely allied to Potentilla (the cinquefoils) and Fragaria (strawberries), and modern molecular analyses of internal transcribed spacer (ITS) DNA sequences have led some authorities to subsume Horkelia within the broadly circumscribed genus Potentilla; however, many regional floras and checklists continue to recognize Horkelia as a distinct genus.
Plants in this genus are low-growing herbaceous perennials with compound leaves and small flowers typical of the rose family. They are characteristic members of western North American flora, with the great majority of species endemic to California and adjacent states. With approximately 45 named species, Horkelia shows its highest diversity in California's varied montane, chaparral, and coastal habitats. Representative members include Horkelia fusca, Horkelia cuneata, Horkelia clevelandii, Horkelia tenuiloba, and Horkelia truncata.
Several Horkelia species serve ecological roles as larval host plants for native butterflies, notably the two-banded skipper (Pyrgus ruralis), which uses H. fusca and H. tenuiloba among others.
Etymology
The genus Horkelia was named by Chamisso and Schlechtendal in 1827, published in Linnaea 2: 26. The name honours Johann Horkel (1769–1846), a German botanist and physiologist.
Distribution
Horkelia is native to western North America, with the overwhelming majority of species occurring in California. Species are found across a range of habitats including montane forests, chaparral, coastal scrub, and meadows, primarily in the Coast Ranges and Sierra Nevada of California, with a smaller number of species extending into Oregon, Nevada, and Baja California.
Taxonomy Notes
The genus Horkelia Cham. & Schltdl. has a disputed circumscription. The GBIF backbone taxonomy treats it as a synonym of Potentilla L., based on molecular phylogenetic analyses (ITS sequence data) that showed the traditional Horkelia to be nested within a broadly defined Potentilla. Under this treatment, Horkelia species are referred to as Potentilla (e.g., Horkelia californica becomes Potentilla californica). Many regional sources, including SEINet and various California flora treatments, continue to recognize Horkelia as a distinct genus. The authorship and original publication are Cham. & Schltdl., Linnaea 2: 26 (1827).
