Thallus: crustose, areolate to sublobate often forming rosettes, thick, ±continuous; prothallus: absent surface: usually ivory, beige, rarely with a pinkish tinge, dull, not smooth, usually strongly pruinose (rarely weak or absent), phenocorticate, esorediate medulla: white, filled with an abundance of calcium oxalate (H2SO4+ needle shaped crystals) Apothecia: lecideine, (0.3-)0.5-1.1(-1.4) mm in diam., immersed, becoming adnate with age margin: black, thin, ±persistent, excluded with age disc: black, usually with fine white pruina, plane, usually becoming slightly convex proper exciple: narrow, poorly differentiated, aethalea-type, 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 strongly carbonized with various amounts of brown and aeruginose pigments (cf. elachista-brown and cinereorufagreen, HNO3+ violet) epihymenium: brown, pigmentation continuous with the outer exciple (HNO3+ violet) hymenium: hyaline, not inspersed with oil droplets; paraphyses: simple to moderately branched, apically swollen, with a brown pigment cap (cf. elachista-brown) asci: clavate, Bacidia-type, 8-spored ascospores: soon brown, 1-septate, oblong to narrowly oblong, very rarely constricted, with obtuse ends, not curved, (13-)16.3-[18.6]-20.9(-25) x (6-)6.2-[7.1]-8(-10) µm (n=60); proper septum: becoming thickened early but only briefly during spore ontogeny (±Physconia-type); ornamentation: microrugulate to faintly striate (best seen in DIC) Pycnidia: rare, urceolate to globose, unilocular; ontogeny similar to the Umbilicariatype conidiogenous cells: mostly terminal, rarely also intercalary (cf. conidiophore-type V) conidia: bacilliform, 3-4.5 x 1-1.5 µm (n=20) Spot tests: usually K+ yellow, rarely K+ yellow-red (crystals), P± yellow, C- , KC-, CK- fluorescence: UV± pale yellow to beige iodine reaction: thallus strongly amyloid Secondary metabolites: atranorin, norstictic acid (traces); 4,5-dichloronorlichexanthone, arthothelin, thiophanic acid (J. A. Elix, HPLC). Substrate and ecology: epilithic, on limestone (HCl+ strongly reacting) or sandstone with some traces of carbonates (HCl+ weakly reacting, rarely HCl-) World distribution: southwestern USA, including Utah, New Mexico, and Colorado Sonoran distribution: northern Arizona (border to Utah, and New Mexico), and southern California. Notes: The thick, areolate to sublobate, strongly amyloid thalli of B. navajoensis with its finely pruinose apothecia and large ascospores are very distinctive and not easily confused with other species.