Rhagadodidymellopsis endocarpi gen. et sp. nov. and Arthopyrenia symbiotica (Dothideomyceta), two lichenicolous fungi growing on Endocarpon species

The lichenicolous fungus Rhagadodidymellopsis endocarpi (Dothideomyceta) growing on the thallus of the terricolous lichen Endocarpon pusillum is described from Spain and Australia as new to science. The new genus and species is compared with other taxa from the genera Didymellopsis and Zwackhiomyces (Xanthopyreniaceae, Collemopsidiales, Dothideomyceta), in particular with D. perigena, a species also having hyaline didymospores and also growing on Endocarpon. Rhagadodidymellopsis endocarpi is characterized by its almost completely superficial stromatic ascomata with a coarse and irregular surface, and an ascomatal wall of very irregular thickness, and ascospores smaller than those of D. perigena. We also compare the new species with other Endocarpon parasites, including Arthopyrenia symbiotica. This is a misunderstood species, originally described as Verrucaria symbiotica, which we also discuss in detail in this study.