We will undertake integrative taxonomic studies of Arctic-boreal taxa of the ''core Stereocaulon'' group of the lichen genus Stereocaulon (Lecanorales, Ascomycota). Our primary focus will be on resolving the S. alpinum/paschale and S. evolutum/saxatile species complexes. The current Stereocaulon taxonomy lacks a unified understanding, species limits remain unclear, and museum specimens frequently occur under wrong names, rendering existing phylogenetic results potentially spurious. Our preliminary ITS phylogeny clearly shows that much hidden diversity exists, including a minimum of ten new species for science in Fennoscandia. To get an overview of this diversity, and for further in-depth studies of selected species complexes, we will produce multi-locus phylogenies including a large number of both freshly collected samples and museum specimens. By combining DNA data with studies of morphology, chemistry and ecology, we aim to determine meaningful species limits in the species complexes and conduct taxonomic treatments accordingly. By using high throughput amplicon sequencing, we can simultaneously sequence DNA from all symbionts. Comparative studies of DNA data from the symbionts will increase our understanding of the Stereocaulon symbiosis and may in turn also have implications for our taxonomic conclusions. In addition to new collections and revision of existing specimens, we will produce identification keys, distribution maps, DNA barcodes, arrange a workshop for dissemination of the new knowledge, and train a B.Sc. or M.Sc. student.