Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.

Thallus: continuous, thin, ±warted or almost granular surface: ±gray, gray-green, or ±brown, without cracks Apothecia: 0.2-0.7 mm in diam., at a very early stage almost flat but soon becoming convex, sessile, without pruina disc: pale brown to brown to black, sometimes piebald margin: at first distinct, level with disc, soon excluded and reflexed, concolorous with disc proper exciple: without crystals, ± olive-brown (K-, N-), pale green (K-, N+ purple), or a mixture of both along rim and sometimes also in upper part, other parts paler epithecium: ±blue-green (K-, N+ purple), ±olive-brown (K-, N-), or a mixture of both; crystals: absent hymenium: 40-65 µm tall, colorless below; paraphyses: 1.5-2.0 µm wide in mid-hymenium; apices: mostly ±clavate or some not at all thickened, 1.5-3 µm wide hypothecium: colorless ascospores: ±acicular, spirally coiled, 17-40 x (2-)2.5-3.5 µm, 3-7-septate Pycnidia: half-immersed, black, 25-75 µm in diam. conidia: bacilliform, non-septate, 6-9 x 1 µm Spot tests: all negative Secondary metabolites: none detected. Habitat and ecology: on ± shaded, sedimentary and igneous rock from sea level to c. 2000 m; in other areas often found on pebbles or occasionally on tree-bark World distribution: North America, Europe, Asia and Africa Sonoran distribution: known from a few scattered localities in central and southeastern Arizona and coastal, southern California. Notes: On a larger geographic scale, S. umbrinum is a very variable species, particularly regarding apothecium pigmentation and thallus structure. A few doubtfully distinct taxa have been described, viz. S. ophiosporum (Hellb.) Hav. and S. perpusillum Lahm ex Körb. The Sonoran material belongs to S. umbrinum in the strict sense.