The lichen symbiosis provides a life form that is successful at colonizing large ranges, and tolerates extremes in climate. How do lichens manage to adapt to a multitude of habitats and climatic conditions? One hypothesis is that the symbiotic phenotype of lichens is able to tolerate various environmental conditions due to its ability to respond to the environment owing to changes in gene expression. Here, we investigate environmental correlations in population structure and gene expression in the lichenized fungus Peltigera membranacea. For our transcriptome study, we focus on genes involved in environmental stress response because these are among the most likely candidates to enable in-situ tolerance in a changing environment.