Xanthoria calcicola Oxner var. calcicola
Thallus folliaceous generally arranged in a rossette, up to 15 cm in diameter, formed, especially at the margin, of 3-5 m wide lobes overlapping each other, folded and wavy, covering from the center with granules and of isidioid warts, upper surface: yellow-orange in areas with little sunlight, bright orange in areas with sun, the center may become more dirty orange-brownish. Apothecia rare and few, sometimes absent, flat bright orange disc, paler margin sometimes crenate. Elliptical, polarilocular, colorless spores, 10-17 x 5-9 µm according to the literature, 12-17 x 6-9 µm according to our measurements. K + purple. Fairly common species found on limestone rocks (as its name suggests!) or very little acid, cement, concrete, very rarely on wood or tree bark, nitrophilic and supporting urban pollution.
The "maritime" forms differ by their occurrence on acidic coastal rocks and are sometimes difficult to separate from certain forms of Xanthoria parietina but this last species has green tones that Xanthoria calcicola does not always (?) orange, it also has more apothecia and no isidioid granulations; and Xanthoria aureola with narrow lobes strap-schaped.