| Summary: | Abstract The shrubby Usnea species of East Fennoscandia and the whole known Usnea flora of British Columbia were studied. Furthermore, the status and distribution of Usnea hirta and U. longissima, which have divergent habitat requirements and distribution patterns, were surveyd in East Fennoscandia. The two species also occur in British Columbia and their chemistry, ecology and distribution were compared in the two study areas. The nomenclature and taxonomy of U. hirta were also revised. Nine shrubby Usnea species were documented from East Fennoscandia and 25 species and species groups were recorded from British Columbia (when U. fulvoreagens and U. pacificana are included as distinct species). U. chaetophora, U. diplotypus and U. nidulans s. lat. were reported as new to North America, whereas U. esperantiana and U. rigida s. lat. were documented for the first time for Canada, and U. ceratina and U. rubicunda are new to British Columbia. U. pacificana was described as a new species from the Pacific Canada and the United States and U. wasmuthii was reported from the states of Washington and Oregon as new to North America. Several taxa were recognized as synonyms and lectotypified in our studies. In total, 21 secondary medullary substances or compound groups were found in the East Fennoscandian and 24 in the British Columbia Usnea species. Salazinic acid is the most common substance in both areas. New chemotypes were found in three shrubby Usnea species in East Fennoscandia and in six taxa in British Columbia. Differences in the chemistry of some species were found when comparing the East Fennoscandian and British Columbia specimens, e.g., in U. hirta and U. longissima. All the East Fennoscandian Usnea species studied have a relatively southern distribution or they are infrequent in northern regions, while most of the surveyed North American species have more or less maritime distribution. All these Usneae are primarily epiphytes and the majority of them prefer well-lit and moist sites.
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