Complex life-cycles are common among fungi. Dimorphism in basidiomycetes involves alternation between a unicellular yeast phase and a filamentous phase, frequently forming basidiomata. Here we have studied the dimorphic life cycle of the lichen-inhabiting basidiomycetes in the Tremella caloplacae species complex, with particular focus on the newly distinguished Tremella parietinae. Using FISH-CLSM, PCR and Sanger sequencing, we have investigated the presence and distribution of the different life-cycle phases of T. parietinae within the lichen Xanthoria parietina, and also conducted an exploratory investigation into the presence of a Tremella yeast phase in other lichens of the Teloschistaceae. We could show that the filamentous phase of T. parietinae is restricted to the hymenium of X. parietina, whereas the yeast phase also grows elsewhere in the thallus. Tremella caloplacae s. str. is detected by PCR in Calogaya, Flavoplaca and Gyalolechia lichens, whereas its basidiomata are restricted to Variospora lichens. These findings suggests different lichen-specificity of T. caloplacae in the different phases of its life-cycle. Key words: Basidiomycete, confocal laser scanning microscopy, fluorescent in situ hybridization, yeast.