Thallus: squamulose-peltate; squamules: 1-2(-3) mm wide, composed of cylindrical to somewhat flattened lobules, erect at first, becoming squeezed aside by growing fruiting bodies, finally often radially arranged, not or sparsely branched, ±cylindrical, sometimes knotty or slightly flattened, straight or bent, lobes 1-1.5 mm long, 0.18-0.3 mm thick, centrally with compact to fairly loose central hyphal strand, 100-170 µm thick, with reticulate anatomy towards the periphery, 40-75 µm thick; upper surface: black, dull; isidia: absent; lower surface: concolorous with the upper surface, attached by central tuft of rhizohyphae; Apothecia: sessile or finally stipitate, marginal or subterminal, 0.4-0.8(-1) mm wide; disc: black (also when moist), at first slightly depressed, finally plane and wide open, sometimes incrusted with dust particles; thalline margin: persisting, 50-100 µm wide, prominent, finally flat; proper exciple: lacking; epihymenium: indistinct but upper parts of hymenium reddish brown; hymenium: IKI+ deep blue, 75-95 µm tall; subhymenium: hyaline, IKI+ blue, 20-25(-50) µm thick, elongated as a stipe into central strand; asci: subclavate or subcylindrical, thin walled, IKI-, but with rather conspicuous gelatinous cap, 8-spored; ascospores: hyaline, simple, broad ellipsoid to subglobose, small, 8-12 x 7-11 µm; Pycnidia: immersed, ellipsoid, c. 200 x c. 50 µm, simple; conidia: filiform, falcate to sigmoid, c. 20-35 x 1 µm; Spot tests: all negative; Secondary metabolites: none detected.; Substrate and ecology: on various rocks in shaded or sheltered microhabitats on boulders and in seepage tracks on rocky slopes (but material from the Old World mainly on calciferous soils); World distribution: Algeria, Morocco, Arabian Peninsula, and North America; Sonoran distribution: central, southern and SE Arizona, SE California, and Baja California.; Notes: Peccania tiruncula is characterized by its short, cylindrical, knotty or somewhat flattened lobes and small, subglobose ascospores. No noticeable differences emerged from the comparison of North American material with specimens from the Old World. In the study area, Peccania tiruncula was found exclusively on rock. In contrast, Peccania subnigra was found almost exclusively on soil crusts.