Xanthoria calcicola Oxner var. calcicola (Taxon Atlantique).

    Thallus foliose, large, to 20 cm, often dense and thick rosette forming (frequently, a second thallus may be observed towards the center with young highly inednted lobes similar to those of Xanthoria aureola, that is very similar), lobes 1-5 mm wide, thick, pleated, especially at the margins of the thallus, apices widened and covered with minute crystals, centre granulose, verrucose, with coarse, coralloid, 0.2-1 mm, wart-like isidia, capitate or with a lobule-like tip, bright yellow-orange, bright orange towards the center and more yellowissh towards margins, possibly green to lemon on shaded areas, lower surface whitish. Apothecia in low numbers (except when isidia are absent), more or less sessile, 2-3 mm diam., disc flat, yellow-orange, exciple irregular often granular or contorted, concolourous. Ascospores ellipsoid, polarilocular, apices distinct, 10-13 x 8-9 µm. Photobiont: trebouxioid. K+ crimson. Common on perching-birds well-lit rocks of aerohaline zone (nitrophile and thermophile) but also found inland. Sometimes found in combination and easily confused with narrow strap-shaped Xanthoria aureola althought some specimen may remain unidentifiable since the transition between specimen without isidia (hot and well-lit locations) to well isidiate Xanthoria aureola is progressive. In fact some confusion is still found in this group and additional research is required to clarify the group structure and detailed classification and phylogeny.
  As a provisional contribution to this question we present here some pictures from Corsica and Sardinia taken on acid rocks and assign them to Xanthoria calcicola var. calcicola  Mediterranean Taxon.  Also difficult to distinguish from poorly fertile specimen of Xanthoria parietina.

Several forms are proposed here:

Xanthoria calcicola var. calcicola (Taxon Atlantique) forme sans isidies  difficult to distinguish from Xanthoria parietina which has thinner lobes with greenish or grayish tinges and generally more numerous apothecia.

Xanthoria calcicola var. calcicola (Taxon Atlantique) forme verruqueuse in which the isidia are replaced by warts suggesting immature apothecia.

Xanthoria calcicola var. calcicola (Taxon Atlantique) forme sur ciment ou béton. Yellow-orange to greenish form.