Abstract
Lichens are a prominent feature of northern conifer forests and a large number of species are thought to be circumboreal. Whether or not circumboreal lichen species really constitute monophyletic groups has seldom been tested. We investigated molecular phylogenetic patterns in the mycobiont of Mycoblastus sanguinarius, a well known epiphytic lichen species of the boreal forest, based on material collected from across the high latitude northern hemisphere. A three-locus dataset of internal transcribed spacer rDNA, translation elongation factor 1-α and replication licensing factor Mcm7 DNA sequences revealed that material treated until now as belonging to M. sanguinarius does indeed form a monophyletic group within the genus and is distinct from a strongly supported Mycoblastus affinis. The M. sanguinarius complex appears closely related to the rare Mycoblastus glabrescens, which is currently known only from the Pacific Northwest and was rediscovered during the present study. However, within M. sanguinarius s.lat. in the northern hemisphere, two deeply divergent and morphologically coherent species can be recovered, one of which matches the southern hemisphere species Mycoblastus sanguinarioides and turns out to be widespread in North America and Asia, and one of which corresponds to M. sanguinarius s.str. Both M. sanguinarius and M. sanguinarioides exhibit additional low-level genetic differentiation into geographically structured clades, the most prominent of which are distributed in East Asia/eastern North America and western North America/Europe, respectively. Individuals from these lowest-level clades are morphologically indistinguishable but chemical analyses by thin layer chromatography revealed that each clade possesses its own fatty acid profile, suggesting that chemical differentiation precedes morphological differentiation and may be a precursor to speciation.