Diversity, dispersal and biogeography of bryophytes (mosses)

Bryophytes disperse by small unicellular spores between 7 mu m und usually less than 100 mu m. A large percentage of species is sterile and propagates vegetatively either by special brood bodies or fragments of whole plants. It is shown that there is no difference in the effectiveness between generative and vegetative propagation. Size and weight of the diaspores suggest that both must easily be dispersed and the species must therefore have wide ranges. This does, however, not result in ubiquitous occurrence. This is only true for part of the species. Many, even sterile species show wide transcontinental ranges. On the other hand, there are many examples of limited to very limited distribution in spite of a rich production of diaspores. These are explained by narrow ecological niches, age of taxa, local extinction or historical events such as ice ages. Conspicuously, species can loose the ability for dispersal for unknown (perhaps genetic) reasons, which may ultimately lead to extinction.