Examination of specimens of Peltigera didactyla, from Africa, Asia, Europe and North America revealed that this sorediate species includes three entities that can be separated on morphological characters. A new species, P. lambinonii, is described from East Africa, and a new combination P. didactyla var. extenuata, is proposed to accommodate morphs from mesic forest habitats in Asia, Europe and North America. Despite this taxonomic reduction, P. didactyla var. didactyla remains a ubiquitous taxon. The former two taxa often produce methyl gyrophorate, which can co-occur with traces of gyrophoric acid. These tridepsides were only rarely detected in var. didactyla; their occasional presence seems to be best explained by hybridization. The taxonomic and ecological significance of these substances is discussed.