The widespread and ubiquitous lichen-forming fungus Protoparmeliopsis muralis is able to form a thallus with Trebouxia species. In this study, several photobiont strains were isolated from different specimens of P. muralis and cultured in vitro. The compatibility of Trebouxia spp. and Asterochloris algae with P. muralis were investigated in in vitro resynthesis experiments and the re-lichenized bionts were observed with the scanning electron microscope. It was found that, in addition to compatible photobionts, also a presumably incompatible Asterochloris sp. was able to interact with the mycobiont. The life strategy that enables the mycobiont to form associations with a wider range of photobionts could be advantageous for the survival of the lichen and successful colonization of new habitats.
