Description: Thallus crustose, episubstratic, smooth to rimose, white to whitish grey, often delimited by a black prothalline line. Medulla white, lacking calcium oxalates, I- Apothecia lecideine, black, (0.3-)0.5-0.8(-1.2) mm across, sessile, with a flat to convex, often pruinose disc, and an initially thick, later thinner and finally excluded proper margin. Proper exciple well developed, 80-125 μm wide in lower part, brown throughout, dispersa-type, N-, K+ yellow or K+ yellow then red (red crystals); epithecium brown, N-, in pruinose specimens inspersed with crystals reacting K+ red; hymenium colourless, not inspersed with oil droplets, (80-)100-110 µm high; paraphyses simple to sparingly branched, the apical cells slightly swollen, 2-4 μm wide, with a dark cap. Asci 8-spored, clavate, Bacidia-type. Ascospores 1-septate, not constricted at septum, brown, ellipsoid to broadly ellipsoid, not curved, (10-)13-16(-18) x (6-)7-8.5(-9.5) µm, Physconia-type when young, Buellia-type when mature, with a rough to faint microrugulate ornamentation. Pycnidia rare, black, immersed. Conidia bacilliform, 6-9 x 0.5-1 µm. Photobiont chlorococcoid. Spot tests: K+ yellow or K+ yellow-orange turning red, C-, KC-, P- or P+ faintly yellow. Chemistry: chemotype 1) atranorin, norstictic and connorstictic acids, plus traces of salazinic and hyposalazinic acids, zeorin and an unknown secalonic acid derivative; chemotype 2) atranorin, traces of norstictic and connorstictic acids, and of a secalonic acid derivative.
Note: on acid and smooth bark in warm-humid areas. All earlier records of this species from upland areas of the Alps and of the northern Apennines (see Nimis 1993: 138) are attributed to Tetramelas chloroleucus following Giralt & al. (2000); some records could refer to the recently-described B. iberica. The species is included in the Italian red list of epiphytic lichens as “Data Deficient” (Nascimbene & al. 2013c).