COMPARISONS BETWEEN THE MOSSFLORAS OF NORTH-AMERICA AND EUROPE

The mossflora of North America and Europa have a common origin; both continents ave been separated for only 50 Million years. Therefore an attempt has been made to compare the differences between the mossfloras of both continents. From North America, 1170 species, 272 genera and 58 families of mosses are knwon, while from Europe we known 1084 species in 232 genera and 51 families. Thus the comparatively small difference of 86 species, 40 genera and 7 families is more in North America than in Europe. A relative comparison of the species per area shows a higher density of species in Europe, which probably is due to the greater ecological differentiation within a smaller area. Sixty-eight genera are represented with the same species in North America and Europe. They probably belong to an old common stock of Laurasian taxa. Sixty-three genera are found only in North America, predominantly neotropical and Pacific in distribution. In contrast, 20 genera are found only in Europe, composed of tropical montane, african and small monotypic genera. Forty-three percent of the North American species are not found in Europe and 30% of the European species are not found in North America. The higher percentage in North America is interpreted as a result of less extinctions in the Pleistocene caused by better availability of refugia. The species endemic to Europe seem to be partly neoendemics originating after separation from North America. Besides the differences in quantity, there are also differences in frequency, habitat preferences, and infra-specific differentiation. More detailed comparisons are provided based on the genera Campylopus and Orthotrichum.