The genetic diversity of photobionts in the lichen Protoparmeliopsis muralis was examined to determine the identity of the photobiont and the level of selectivity for the photobiont by the mycobiont. Forty ITS rDNA sequences of photobionts from thirty nine specimens of Protoparmeliopsis muralis have been determined. The photobiont species were identified both by direct comparison with the available sequences and by phylogenetic analysis. The sequences obtained from P. muralis specimens belonged to different Trebouxia clades. The most common photobionts were T. incrustata and an unidentified lineage, here named as “muralis I”. Less common photobionts were T. asymmetrica and T. gigantea. Two unidentified Trebouxia spp. and a photobiont that belonged to the clade that includes T. impressa, T. flava and T. potteri were also found to be associated with P. muralis. Such flexibility has not been reported to date. Moreover, two different photobionts were found in a single specimen. They belonged to the T. gigantea clade and “muralis I” lineage. The low level of selectivity with respect to the photobiont may constitute an important aspect in that Protoparmeliopsis muralis is one of the most successful urban lichens in the world.