Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: adnate to rather loosely adnate, appressed to occasionally subpulvinate, foliose, up to 6 (-9) cm diam., lobate lobes: short and rounded to somewhat elongate, often distinctly flabellate at the end, contiguous or becoming imbricate, (0.4-) 0.8-1.5 (-3) mm broad, flat to slightly convex or concave upper surface: dark olive-brown to blackish, infrequently paler olive to olive-brown, smooth or occasionally somewhat pitted near the lobe-ends, inward smooth to variously rugulose and/or warted, especially on larger thalli; frequently shiny, especially near the periphery, only occasionally dull throughout, rarely lightly pruinose; pseudocyphellate, the pseudocyphellae small and obscure to frequently quite distinct, submarginal on the lobes soredia: granular to isidioid, dark gray to black (appearing white sometimes when abraded or eroded), in laminal and submarginal soralia arising in part from the pseudocyphellae; soralia: punctiform to capitate and frequently short stipitate but sometimes eroded and crateriform, remaining discrete or becoming confluent in older parts, lower surface: very dark brown to black, flat to weakly channeled, smooth to rugulose, dull or slightly shiny in part; moderately rhizinate, the rhizines concolorous with the lower surface Apothecia: infrequent, up to 3 (-5.5) mm diam., sessile or very short stipitate, somewhat concave or flattening, the margin usually partly to completely sorediate, occasionally remaining entire but then usually rugose, pseudocyphellate asci: clavate, 8-spored ascospores: ellipsoid, 9-12.5 x 5-7 µm Pycnidia: rare, immersed conidia: acerose to almost fusiform, 6-7.5 x 1 µm Spot tests: cortex K-, C-, KC-, P-, HNO3-; medulla K- or rarely dingy, C -, KC- or rarely KC+ very faint rose, P- Secondary metabolites: perlatolic and stenosporic acids (both major). Substrate: rocks, extremely rare on bark or old wood World distribution: circumboreal, central and northern Europe, Siberia, Central Africa, and North America Sonoran distribution: infrequent in montane areas from 2,000 to 3,000 m. Notes: The only other sorediate, and obligately saxicolous species in this genus occurring in the study area is M. tominii, which usually has much more conspicuous pseudocyphellae, and has a distinctly C+ reddish medullary reaction. Closely related M. sorediata is not yet known from the Sonoran region, although it does occur in western North America south to Colorado and Oregon, and might still be found here. It can easily be distinguished by the lack of pseudocyphellae, and presence of discrete soralia, primarily on the ends of short, erect, lateral lobes (Esslinger 1977).