Umbilicaria grisea Hoffm.
Thallus 1-4 cm diam., single-lobed, potentially forming colonies, flat or undulating, lobe margins rounded or lacerate, sorediate, upper surface pale grey, rimose to pruinose, pale grey, pale grey-brownish, lower surface markedly rimose-warted without or with few rhizinomorphs, margin brown, center whitish. Apothecia extremely rare in our prospection area, 0.5-1.5 mm diam., gyrose, black. Ascospores simple, ellipsoid, 14-16 x 7,5-9 µm. Photobiont: chlorococcoid. Medulla : C+ red, K-, KC+ red, Pd-. Not particularly maritime, but shows oceanic trends in our region, often in water-seapage tracks of vertical walls of large rocks.
N.B. Very similar species and often confused with Umbilicaria freyi which is a more thermophilic species whose lobes have schizidia at the margin.