Blastenia festivella (Nyl.) Vondrák forme Atlantique Cf. = Caloplaca limitosa forme Atlantique Cf.

     This form differs from the Mediterranean taxa of Caloplaca limitosa only by its occurrence on the very sunny coastal rocks of the shores of Brittany. It closely resembles some forms of Caloplaca crenularia that may come nearby but differs in a very distinct blackish hypothallus which is very visible (even in the slits of the thallus) when mosaic with itself or with other species. N.B. It could also be a form of Caloplaca crenularia because there is sometimes a blackish hypothallus in this last species in contact with another species of crustacean lichen but this hypothallus does not exist in the case of mosaic.