Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2004. Lichen Flora of the Greater Sonoran Desert Region. Vol 2.
Thallus: umbilicate, monophyllous, +circular, rigid, often with ragged margin, 1-3(-6) cm in diam. upper surface: pale to dark gray, dull, smooth to minutely roughened, with a white necral layer centrally, a few short folds or ridges or numerous fine striae radiating from the umbo medulla: white lower surface: gray or patchy black where covered with thalloconidia, smooth, dull Apothecia: not common, black, leiodisc asci: clavate, 8-spored ascospores: simple, hyaline, narrowly ellipsoid, 10-20 x 3-7 µm Thalloconidia: simple, dark brown, released directly from patches on the lower cortex Spot tests: medulla K-, C+ red, KC+ red, P- Secondary metabolite: gyrophoric acid, Substrate and ecology: on boulders in the boreal or low-alpine zone World distribution: Europe, Asia, Australia and North America Sonoran distribution: rare, only found once in southern Arizona. Notes: Umbilicaria subglabra is common in the European Alps and the Pyrenees, but was only recently recognized for North America. The smooth upper surface and thalloconidia-covered lower surface of U. subglabra separates it from U. krascheninnikovii which has prominent ridges on the upper surface and no conidia on the lower surface.