Aim: Fungi show a variety of reproductive strategies, switching between haploid and diploid forms to benefit from both, the acquisition of genetic variability through sexual reproduction and rapid population growth via asexual reproduction. Throughout the history of lichenology, lichen reproductive modes (e.g., soredia, isidia, apothecia) have been considered as important characters to circumscribe species. This includes the globally vulnerable lichen genus Cetrelia, where morphologically similar taxa with differing reproductive strategies were regarded as ‘species pairs’. We aim to test the historical species concept and evaluate factors responsible for the expression of differing fungal reproductive modes in the lichen genus Cetrelia. Location: Global, covering Nearctic, Palearctic and Indomalayan biogeographic realms. Methods: The morphology and chemistry of 601 samples representing 18 species were examined under the microscope and using thin-layer chromatography. The Cetrelia species concept was assessed by multi-locus phylogenetic analyses (nrITS-IGS-RPB1-MCM7) based on maximum likelihood and Bayesian inference approaches. The correlation of reproductive traits, lichenized fungal and algal genetic identity, macroclimate, geography, habitat, secondary metabolites and substrate were evaluated using principal component analysis and variance partitioning analyses. Results: The phylogenetic analyses indicate that ‘species pairs’ in Cetrelia are genetically indistinguishable, and primarily sexually reproducing species form a monophyletic clade with their counterpart. Variance partitioning analyses suggest that the reproductive modes of Cetrelia are driven by macroclimate, mycobiont, geography, photobionts and habitat. Main Conclusions: Our work highlights the potential risks of climate change, especially the change of precipitation regimes affecting lichen reproduction and dispersal and the need to conserve habitats in south-east Asia where the lichen genus Cetrelia diversity is largely restricted to. Keywords: climate | fungal reproductive modes | lichenized fungi | reproductive ecology | species pairs | symbiosis.