Xanthoria aureola (Ach.) Erichs. forme saxicole pseudoisidiée.

     This form occurs on concrete posts, the tops of cement parapets by the sea, but also on low acid rocks and walls in well exposed but dry places and generally in the sun. Compared to Xanthoria aureola s.l. it presents isidia (or better pseudoisidia) in greater or less number and especially towards the center of the thallus. Apothecia are rare and the somewhat "embossed" lobes with an upward curved margin are uniformly orange to yellow in color. It is quite rare in our prospection region where it often shares this type of habitat with Xanthoria parietina s.l.,. N.B. To distinguish it from Xanthoria calcicola var. calcicola (Taxon Atlantique) forme sur ciment ou sur béton, it is necessary to take into account the coloring: in this last species it can become greenish in the shade, more the lobes are less strip and their surface is not "embossed "; Xanthoria parietina s.l. has larger, unembossed lobes and almost always has a glaucous gray-greenish coloration in places (often roundish towards the margin) and has no isidia.

N.B. This form formerly reported to Xanthoria calcicola var. calcicola (Taxon Atlantique) forme sur ciment ou sur béton,, due to the presence of isidia (or pseudo-isidia) has been sequenced (specimens of Concarneau) and would be related to an isidial form (aborted apothecia?) of Xanthoria aureola, which after re-examination is very plausible due to the slightly embossed appearance of the relatively narrow lobes and the absence on the ground of greenish specimens (for those in the shade), additional analyzes (pigments, photobionts ) are in progress.