Thallus: crustose, composed of scattered areoles or forming a continuous crust, rimose to areolate, often verrucose; prothallus: black, sometimes developed between areoles surface: smooth, white or grayish white, esorediate medulla: white, lacking calcium oxalate (H2SO4-) Apothecia: lecideine, 0.2-1 mm in diam., soon sessile disc: black, epruinose, flat, soon convex margin: black, initially distinct but later excluded proper exciple: 25-45 µm thick, lacking secondary metabolites; differentiated into a broad, dark brown outer part with carbonized cells (<7 µm, HNO3-), and a pale inner part, transient with the brown, <200 µm thick hypothecium (HNO3-) epihymenium: brown, pigmentation continuous with the outer exciple (HNO3-) hymenium: hyaline, strongly inspersed with oil droplets, 85-105 µm tall; tips of paraphyses: ±4.5 µm wide with distinct apical caps asci: clavate, Bacidia-type, 58-78 x 15-26 µm, 8-spored ascospores: soon brown, submuriform, with <12 cells in optical section, ellipsoid, (19-) 20.2--23.8(-28.5) x (9-)10-[11.5]-13(-15) µm, walls and septa lacking uneven thickenings, proper wall c. 0.4 µm thick, lacking a perispore, ornamentation: not visible in DIC Pycnidia: rare, immersed, with upper part protruding, wall mainly pigmented in upper part conidia: bacilliform, c. 4-6 x 1 µm Spot tests: thallus K+ yellow, C-, P+ yellow; medulla K-, C-, P- fluorescence: UV- iodine reaction: medulla non-amyloid Secondary metabolites: atranorin and sometimes placodiolic acid. Substrate and ecology: on bark and wood of conifers, rarely on broad-leaved trees, in montane forests of the Rocky Mountains and the mountain ranges farther west World distribution: western North America (Rocky Mountains) Sonoran distribution: southern California (San Bernardino Mountains, Los Angeles Co.). Notes: Buellia penichra is characterized by submuriform spores lacking a perispore. The species is similar to Buellia muriformis, but has smaller, early pigmented spores and thalli that lack some secondary substances (brialmontin 1 and 2 and isousnic acid). The two species also show different distribution patterns and habitat preferences. Buellia muriformis is absent from the Sonoran Region. It occurs further to the northwest, generally at low altitudes, often close to the coast. In contrast, B. penichra is a montane species.