Synonyms: Acarospora scyphulifera Vain.; Acarospora smaragdula subsp. smaragdula var. scyphulifera (Vain.) Clauzade & Cl. Roux; Acarospora smaragdula var. rhagadiza (Nyl.) Clauzade & Cl. Roux; Silobia rhagadiza (Nyl.) M. Westb.
Distribution: S - Camp (Westberg & al. 2011).
Description: Thallus crustose, episubstratic, areolate, the areoles irregular to angular in outline, contiguous or sometimes dispersed, separated by broad cracks; fertile areoles 0.7-1.5 (-2) mm wide, dirty greyish brown, dark brown or pale rusty-red, dull, epruinose, usually flat, sometimes convex or with slightly upturned margins. Epicortex absent or very thin; cortex paraplectenchymatous, of isodiametric cells, the uppermost ones with red-brown to dark brown caps, without crystals; algal layer interrupted by thick anticlinal bundles of medullary hyphae; lower cortex absent. Apothecia cryptolecanorine, 0.15-0.55(-0.65) mm across, immersed, 1-4 (-6) per areole; with a reddish brown to brown (reddish when wet), smooth, epruinose disc surrounded by a distinct, slightly raised, pale brown to blackish parathecial margin, the thalline margin poorly developed. Proper exciple colourless, but uppermost cells with dark brown caps; epithecium yellow-brown to dark red-brown; hymenium colourless, 110–160 μm high; paraphyses sparingly branched and anastomosing, 1-2 μm thick, the apical cells cylindrical to clavate; hypothecium colourless to greyish or yellowish, densely inspersed with oil droplets. Asci 100-200-spored, clavate, the apical dome K/I-. Ascospores 1-celled, hyaline, ellipsoid, 2.5-3 x 1–1.5 μm. Photobiont chlorococcoid. Spot tests: thallus K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.
Note: optimum on basic siliceous rocks, usually not far from the coasts; a very variable, mainly western species in Europe, also reported from Mt. Vesuvius.