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 loosely adnate ± appressed throughout or somewhat ascending at the periphery, foliose, up to 6 cm diam., lobate lobes: short and rounded to somewhat elongate, ± contiguous to imbricate, 2-4 (-5) mm broad, ± flat upper surface: olive-brown to reddish brown, smooth to weakly wrinkled or pitted on the lobe-ends, inward smooth to rugose, dull throughout or slightlv shiny on some lobe ends, with usually rather numerous small, hyaline cortical hairs; without typical pseudocyphellae, but lobe edges in places with linear, sometimes pale abrasions (like those of M. glabra) isidia: sparse or more abundant, largely marginal to more often evenly scattered over the thallus, cylindrical, simple or much branched, up to 0.8 mm long and 0.05-0.2 mm diam., usually with many cortical hairs (but see discussion) lower surface: pale tan to black or mottled; smooth to rather strongly wrinkled, especially on the lobe-ends, ± dull; moderately to somewhat sparsely rhizinate, the rhizines concolorous with the lower surface or darkening Apothecia: frequent, up to 3.5 mm diam., sessile to very short stipitate, concave when small, becoming irregularly flattened with age, the margin at first entire, becoming ± crenulate or lacerate, densely hairy, sometimes becoming sparsely isidiate asci: clavate, 8-spored ascospores: ellipsoid, 11.5-14 x 5.5-8 µm Pycnidia: infrequent, immersed conidia: ± acerose to filiform, 6.5-8 (-10) x c. 1 µm Spot tests: cortex K-, C-, KC-, P-, HNO3-; medulla K-, C+ red, KC+ red, P- Secondary metabolite: lecanoric acid. Substrate: bark or rocks World distribution: Arizona, Utah, northern India, Pakistan, Nepal Sonoran distribution: known from a single locality in Gila County, Arizona. Notes: This species has not previously been reported for North America, and the identification of the single specimen from Arizona has to be considered tentative. It is a well developed specimen, and although it matches most characters observed in the original Asian material, it lacks the usually numerous cortical hairs of those specimens. However, the pattern of occurrence of these hyaline cortical hairs is variable enough in other species of this group (M. glabra, M. glabroides, M. subargentifera), that their absence from one specimen is inconclusive. There is also one scrappy specimen from Utah (San Juan Co., Devils Canyon, Nash 14956 [ASU]) that appears to be this same taxon. If more material is found, and the lack of hairs is constant, a more careful comparison may require recognition of a new taxon. Because of the isidia, this species, especially when lacking cortical hairs, is most likely to be confused with M. fuliginosa, but the isidia are coarser, more branched, and rounded at the end (instead of tapered), and the form of the lobes (e.g. ± up-turned lobe margins with pseudocyphelloid lines on the edges) clearly indicate a closer relationship with M. subargentifera. That species does sometimes have rather strongly isidioid soredia (when the pustules dont break open in the usual way) and such specimens could be confused with M. villosella, but the cortex of these pseudoisidia in M. subargentifera is dull and unlike that of the rest of the cortex on the upper surface.