Umbilicaria crustulosa (Ach.) Lamy

      Thallus folliaceous formed of a single lobe of 3-5 cm, sometimes fissured or split and then giving the impression of being polylobed, umbilicated and fixed by its base to the substrate, upper surface smooth but sometimes finely chapped, whitish, dirty whitish, gray-whitish, pale gray-brownish, often with pinkish tones, sometimes brownish towards the margin, pale underside: pale brownish-gray with pale brownish rhyzomorphs. Apothecia black, usually numerous, in button; partially immersed in the thallus at the beginning then as posed on the thallus, 2-4 mm in diameter, typically umbilicated with a small protuberence in the center and a more or less notched crown margin. 8-spore asci. Spores colorless, broadly elliptical, simple but becoming mural with age, 18-24 x 13-18 µm. C + red, K-, KC + red, P-. Saxicolous species, a little nitrophilous coming on the siliceous rocks of the hills and the mountains, more rarely on the stony ground. Cf. Umbilicaria cylindrica whose thallus has black rhizines and whose apothecia are a little sessile and gyrous.