Description: Thallus foliose-umbilicate, attached by a central holdfast, monophyllus, 0.42-1.78 mm thick when dry, 0.43-0.72 mm thick when wet, the lobes 13-42 mm wide, with usually down-rolled margins. Upper surface grey-pruinose, slightly to distinctly areolate. Lower surface pale brown, distinctly papillose, erhizinate. Upper cortex 90-260 µm thick, brownish in the uppermost 10-30 µm, with an epinecral layer of air filled hyphae; lower cortex 40-90 µm thick, consisting of ca. 8 cell layers; medulla white to patchily pigmented, 90-500 µm thick, I-. Perithecia numerous, immersed in the thallus and scattered over almost the whole upper surface (appearing as black dots), without involucrellum. Exciple colourless except in the brown uppermost part; hamathecium of periphyses and periphysoids, interascal filaments absent; hymenial gel hemiamyloid. Asci 8-spored, cylindrical-clavate, fissitunicate, the wall thickened above, not amyloid. Ascospores 1-celled, hyaline, ellipsoid, 8.5-14.0 x 4.5-6 µm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: a morph with thick thalli and a distinctly papillose lower surface, found on calcareous or basic siliceous rocks, usually in long-time dry localities, with several records in the western and eastern Alps (France, Austria). According to Heiðmarsson (2017) it should be considered as a synonym of D. miniatum. To be looked for in Italy.