Thallus: crustose, areolate, thin to moderately thickened, ±continuous; prothallus: conspicuous black, often strongly developed and growing between the areoles (forming a hypothallus), rarely only surrounding the thallus outline surface: usually deep brown, rarely olive brown, dull, rarely ±shiny, smooth, epruinose, phenocorticate, esorediate medulla: white, lacking calcium oxalate (H2SO4-) Apothecia: lecideine; (0.2-)0.3-0.4(-0.5) mm in diam., remaining immersed to indistinctly adnate margin: black (or color masked by grayish remains of necrotic thalline material, thalline veil), prominent, usually persistent, rarely excluded with age disc: black, epruinose or rarely with faint, white pruina, plane, rarely becoming slightly convex with age proper exciple: narrow, poorly differentiated, aethaleatype, inner excipular hyphae narrow, hyaline, prosoplectenchymatous (textura oblita), often reduced, similar in structure and orientation to the paraphyses, transient with the deep reddish brown hypothecium (leptoclinoides-brown, textura intricata), outer excipular hyphae parallel, moderately swollen (textura oblita) and usually strongly carbonized with various amounts of a brown pigment (cf. elachista-brown HNO3-) epihymenium: brown, pigmentation continuous with the outer exciple (HNO3-) hymenium: hyaline, not inspersed with oil droplets; paraphyses: simple to moderately branched, apically swollen, with a brown pigment cap (cf. elachista-brown) asci: clavate, Bacidiatype, 8-spored ascospores: soon brown, 1-septate, oblong to ellipsoid, usually not constricted, with obtuse ends, not curved, (9-)9.4-[10.4]-11.3(-15) x (5.5-)5.8-[6.2]-6.7(-8) µm (n=60); proper septum: narrow, not thickening during spore ontogeny (±Buellia-type); ornamentation: not visible in DIC Pycnidia: rare to common, urceolate to globose, unilocular; ontogeny similar to the Umbilicaria-type conidiogenous cells: mostly terminal, rarely also intercalary (cf. conidiophore-type V) conidia: bacilliform, 4.5-7 x 0.5-1 µm (n=20) Spot tests: because of the dark thallus usually only observed if tested in the compound microscope, K+ yellow to red (±crystals), P- or + faintly yellow, C-, KC-, CK- fluorescence: UV- (dark) iodine reaction: medulla non-amyloid Secondary metabolites: norstictic with connorstictic acid, 2'-O-methylperlatolic acid (J. A. Elix, HPLC). Substrate and ecology: epilithic, on a wide variety of siliceous (HCl-) rock, typically on shaded and ±sheltered boulders and cliffs in montane areas World distribution: rare in Mediterranean Europe and southwestern USA Sonoran distribution: common and widely distributed in Arizona, Sonora, and Chihuahua, also at higher elevations in Baja California Sur. Notes: Buellia tyrolensis is a very common species in montane areas throughout the Sonoran Region. With its distinctly areolate thallus and its conspicuous black hypo-thallus delimiting separate areoles, it is a superficially similar species to B. spuria or B. stellulata. Unlike these two species, B. tyrolensis is, however, always deeply brown to olive brown, and lacks aeruginose pigmentation of the outer exciple or epihymenium. According to Bungartz (2004), Buellia tyrolensis is the correct spelling and must not be changed to "tirolensis". The page number for the original description is sometimes incorrectly given as 460 and the year of the publication is sometimes incorrectly given as 1865.