Description: Thallus crustose, episubstratic, rather thick, whitish to dirty yellowish brown, areolate, the areoles irregular in outline, flat to slightly convex, separated by deep cracks. Medulla white, I+ blue. Apothecia lecideine, black, 0.3-0.8(-1) mm across, subimmersed to subsessile, with a soon convex, usually epruinose disc, and a soon excluded proper margin. Proper exciple brown in outer part, paler within; epithecium brown; hymenium colourless, K/I+ blue; paraphyses simple, slightly capitate; hypothecium pale to dark brown. Asci 8-spored, clavate, Bacidia-type. Ascospores 3-septate, brown, ellipsoid, slightly curved and bean-shaped, 10-16 x 3-6 μm, with a minutely verrucose ornamentation more evident at both ends. Photobiont chlorococcoid. Spot tests: K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: an apparently widespread but rare, or at least rarely distinguished, silicicolous species characterised by ornamented, four-celled spores with transverse septa only, and by the I+ blue reaction of the medulla. It is very closely related to (and often synonymized with) the calcicolous D. dispersum, which differs in the less evidently ornamented spores and in the ecology.