Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: narrow-lobed, orbicular to irregular, up to 3 cm diam., firmly adnate lobes: up to 1 mm wide but rarely exceeding 0.5 mm, convex and adnate the tips, usually distinctly discrete and deeply divided, eciliate upper surface: gray to very dark gray, not or weakly white spotted; soredia and isidia absent upper cortex: paraplectenchymatous medulla: white lower cortex: paraplectechymatous with thick-walled, partly irregular cells, the cortex distinctly delimited from the medulla lower surface: white to brownish with concolorous or darker, ± abundant rhizines Apothecia: usually abundant, up to 1.5 mm diam.; margins crenulate; disc: dark brown to black, without pruina ascospores: brown, 1-septate, Pachysporaria-type (15-) 19-24 (-28) x (7.5-) 9.5-12.5 (-14) µm Pycnidia: ± abundant, immersed, rounded, sometimes confluent and forming aggregates conidia: subcylindrical, 4-6 x 1 µm Spot tests: upper cortex and medulla K+ yellow, C-, KC-, P+ yellow Secondary metabolites: upper cortex with atranorin; medulla with atranorin, zeorin and triterpenes. Substrate and ecology: growing on ± exposed rocks or on mosses on rocks World distribution: northern South America and Mexico Sonoran distribution: known only from two localities, Baja California Sur, Sierra de la Laguna at 1800 m and in Sonora W of Yecora at 1700 m. Notes: This species is recognized by its narrow, distinctly discrete and deeply incised lobes and the abundant, small, crenulate apothecia. It is similar to P. alba, which has ± flat, broader lobes, and mainly grows on bark. The material from Baja California has somewhat smaller spores than the South American material, but this is regarded as being a result of a more northerly site.