Basidiomycete yeasts as hidden partners in ascomycete lichens

For 140 years lichens have been described as a symbiosis between a fungus and photosynthesising partners. Lichens repeatedly host a wide range of additional fungi and bacterial communities but their role has been considered nonessential for the formation of the symbiosis. We found that previously unknown basidiomycete fungi (Cyphobasidium spp.) are widespread components of several macrolichens and that their abundance explains phenotypic variation in some cases. We could locate these fungi into the lichen cortex. With this study, the role and diversity of the different organisms involved in one of the oldest known symbioses need to be reconsidered.