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 to irregular in shape, with characteristic sieve-like perforations along the margins that are often shredded, 2-6 cm in diam. upper surface: medium to dark brown, often shiny, criss-crossed by dark fissures among slightly bumpy areolate-like structures medulla: white lower surface: beige to light brown, smooth to coarsely papillate, with trabeculae (plate-like structures) radiating from the umbilicus, rhizinomorphs scattered or dense Apothecia: common, black, partially immersed to sessile, gyrose, up to 2 mm in diam. asci: clavate, 8-spored ascospores: hyaline, simple, ellipsoid, 8-12 x 4-6 µm Spot tests: medulla K+ yellow, C+ red or C-, KC+ red or KC-, P+ orange Secondary metabolites: gyrophoric, lecanoric and stictic acids. Substrate and ecology: on siliceous rocks World distribution: Europe, Asia and North America. Sonoran distribution: upper conifer or alpine vegetation zones of southern California and Arizona. Notes: Umbilicaria torrefacta, a typically arctic/alpine species, is separated from the typically lower elevation U. angulata by its circular versus respectively angular apothecia. In addition, the occurrence of perforate margins is typical in U. torrefacta.