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 throughout or ascending somewhat at the periphery, foliose, up to 11 (-15) cm diam., lobate lobes: short and rounded to slightly elongate, contiguous to imbricate, 2-5 (-7) mm broad, ± flat upper surface: olive-green to dark olive-brown, sometimes tinged yellowish or reddish, smooth to somewhat wrinkled or pitted on the lobes, inward soon becoming ± strongly rugose or irregularly papillate, occasionally foliolate; ± dull throughout or occasionally rather shiny on the lobe-ends or over larger areas, occasionally lightly pruinose, bearing tiny, hyaline, cortical hairs, these dense to sparse (rarely totally absent) but usually present at least on some lobe ends and apothecial margins; pseudocyphellae limited to the warts of the upper surface, but, on many thalli, there are pale, pseudocyphelloid lines on the extreme outer edge of the lobes lower surface: dark brown or black, often paler at the margin, smooth to uneven or locally wrinkled, dull to slightly shiny; moderately rhizinate, the rhizines concolorous with the lower surface Apothecia: common, up to 8 (-11) mm diam., sessile to short stipitate, at first concave, becoming irregularly flattened with age, the margin entire when young, soon becoming crenate, crenate-papillate, or even reticulately ridged, the papillae or ridges bearing ± obscure pseudocyphellae, nearly always bearing cortical hairs asci: clavate, 8-spored ascospores: ellipsoid to broadly ovoid, 11-15 x 5.5-8 (-10) µm Pycnidia: common, immersed conidia: ± acerose or cylindrical, (6.5-) 8-9 x 1 µm Spot tests: cortex K-, C-, KC-, P-, HNO3-; medulla K-, C+ rose or red, KC+ red, P- Secondary metabolite: lecanoric acid. Substrate: bark, occasionally on rocks World distribution: SW North America, southern Europe, northern Africa, Asia Sonoran distribution: common in California oak forests, known from a single locality in Arizona. Notes: The other fertile, corticolous species occurring in the Sonoran Region, M. subolivacea and M. multispora, are easily distinguished by their thinner thalli and C- medulla. Rare saxicolous specimens of M. glabra are most likely to be confused with M. glabroides, which can be identified by its more lobulate/subpanniform habit, with lobes that are commonly somewhat to strongly reticulately pitted and have few or no cortical hairs, and its sparse or absent apothecia.