Milospium graphideorum Cf. parasite de Dirina massiliensis forma sorediata
Unlichenized lichenicolous fungus.
On this host, at first small black spots may be seen towards the thallus center and a centrifugal infestation is then observed that invades the whole thallus and completely destroys it at the end of the process. Rather common on this host in this type of habitats: here an old sheltered wall on the North side of a chapel.
N.B. This interpretation is provisional because it is probably another taxon that may be related to Reichlingia leopoldii.