1.5. Distribution

Usnea is a cosmopolitan genus occurring on all continents. Species diversity, however, is low in arid and arctic areas and is highest in humid regions of temperate latitudes. The East Fennoscandian and British Columbia Usnea floras mostly consist of species that are widely distributed in the Northern Hemisphere, but also contain some species that are nearly cosmopolitan.

Among the East Fennoscandian Usnea flora U. hirta and U. longissima represent the only species which also range to the Southern Hemisphere. U. hirta has continental tendencies, but it has been found on almost every continent (Clerc 1997). The species occurs nearly in the whole Europe (Poelt 1969) and its North American range extends from the boreal zone to Mexico (Thomson 1984). U. longissima has oceanic tendencies (Ahti 1977) and occurs from boreal to tropical regions. The species is extinct or nearly extinct in most parts of Europe (Sérusiaux 1989). The richest European populations are in Scandinavia, especially in Norway (Tønsberg et al. 1996). U. longissima is still locally common in North America occurring along the Pacific coast from northern California to Alaska, in the eastern parts of Canada and in the north-eastern United States (Brodo et al. 2000). The species, however, has also declined in North America (Bennett 1995).