Gard. Dict. Abr. ed.4, vol. 3. 1754
Boreal North America, southward in w Cordillera, Eurasia.
Species 15–18 (1 in the flora).
North American Petasites is taxonomically difficult as a result of low variability in reproductive morphology and a high degree of leaf polymorphism. The conservative reproductive structures across all taxa make identification almost impossible without foliage and, unhappily, flowering usually occurs prior to emergence of basal leaves. Further compounding the taxonomic confusion is the apparent intergradation of many of the different leaf forms as well as leaf morphologies being subject to environmental plasticity.
Using morphometric, isozymic, and chromosomal data as well as crossing studies and observations of field and herbarium specimens, relationships of the various entities have been interpreted by D. M. Cherniawsky and R. J. Bayer (1998, 1998b). North American Petasites has been shown to be loosely comprised of four polymorphic groups. Close relationships among the groups were evident in all analyses by Cherniawsky and Bayer and suggested rapid and recent morphologic and genetic divergence in North America. They postulated that groups within North American Petasites have not yet reached a level of differentiation characteristic of distinct species. On this basis, North American Petasites is treated here as one polymorphic species with four infraspecific taxa, one a hybrid.
Characters used in this treatment are those found to be the most taxonomically discriminating by D. M. Cherniawsky and R. J. Bayer (1998c), although there is a high degree of overlap of ranges across all taxa. Morphologic variation is continuous for most reproductive characters. Values for reproductive characters are mostly continuous with only a few extreme ranges providing some taxonomic demarcation. Although leaf characters were shown to be the most reliable, it is recommended that a combination of both flowers and leaves be used for accurate identifications.
In cooler regions of the northern hemisphere, Petasites glacialis and P. gmelinii, both with yellow corollas and 1[–3] heads per array, approach the Bering Strait in northeastern Siberia; they apparently do not reach Alaska (E. Hultén 1968).
Two relatively large-leaved exotic species of Petasites are sold as ornamentals: the European P. hybridus (Linnaeus) Gaertner, Meyer, & Scherbius, with purplish florets and reniform to orbiculate-cordate, shallowly angular-lobed, finely and unevenly toothed leaf blades 10–90(–100) cm wide; and the Asian P. japonicus (Siebold & Zuccarini) Maximowicz, with creamy white to whitish corollas and reniform-cordate, unlobed, finely toothed leaf blades 15–30(–150) cm wide. They occasionally escape cultivation (e.g., P. hybridus established in Michigan).
The rhizomes, petioles, leaf blades, and young flower stalks of some species of Petasites are (or have been) used for food in various ways and their ashes are used as a salt substitute. In folk medicine, some species of Petasites are used as antiasthmatics, antispasmodics, and expectorants and in salve or poultice form.
Measurements in the following key leads and descriptions are based almost wholly on North American specimens.
|Author||Randall J. Bayer +, A. Linn Bogle + and Donna M. Cherniawsky +|
|Common name||Butterbur +, coltsfoot + and pétasite +|
|Etymology||Attributed to Dioscorides, Greek petasos, broad-brimmed hat, alluding to large basal leaves +|
|Illustrator||Yevonn Wilson-Ramsey +|
|Reference||cherniawsky1998a +, cherniawsky1998b +, cherniawsky1998c + and toman1972a +|
|Taxon name||Petasites +|
|Taxon parent||Asteraceae tribe Senecioneae +|
|Taxon rank||genus +|
|Volume||Volume 20 +|