The aim with this study is to determine genetic variation, dispersal potential and the migration history to Sweden since the last glaciation of the rare lichen Cliostomum corrugatum, a crustose epiphytic lichen with a grey greenish thallus,conspicuous light yellow to light brown apothecia and black pycnidia. Collections were made in January and February in 2005 at five sites in Östergötland, Sweden. The most frequent common habitat for Cliostomum corrugatumis on Quercus and sometimes also on other deciduous trees for example Ulmus and Fraxinus. On the tree trunk it is the rough bark it prefers and the flat terminal parts of the bark structure and not on the sides of the cracks. The main distribution of Cliostomum corrugatum is in Europe but a satellite population has been found on the west coast of North American in British Columbia. It is red listed in Sweden, with the status near threatened. Three sequences SSUintron, IGS and ITS were studied and the two latter appear to lack genetic variation. A total of 85 sequences with a length of 614 base pairs were studied of a rRNA SSU intron. Eleven haplotypes were detected, two was common 46 and 30 in numbers respectively and was present on all five localities the other nine were detected only once each. The two common haplotypes are in the centre of a rooted net work and the rare in the periphery. Cliostomum corrugatum does not seem to have problem with its dispersal. The limiting factor seems to be the occurrence big oaks. In the studied area the smallest tree trunk diameter that Cliostomum corrugatum was found on is 0,65 metre. The tree with the largest diameter in the research area is 1,65 metre. A tree that is 0,65 metre in diameter is at least 100 years old. Oaks of this age are scarce and this is one of the reasons for the rareness of Cliostomum corrugatum. When Cliostomum corrugatum colonized Sweden after the last ice age, all eleven haplotypes may already have existed. However, it is possible, that some haplotypes evolved after the migration to Östergötland.