Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2002. Lichen Flora of the Greater Sonoran Desert Region. Vol 1.
Thallus: variable, verrucose, wrinkled or rimose-plicate to rimose, with thin to thick verrucae; margins: entire, unzoned upper surface: yellowish gray, greenish gray to creamish, smooth to rugose, dull, epruinose; lacking soredia or isidia fertile verrucae: concolorous with thallus, pertusariate, hemispherical to irregular, flat-topped, smooth or deformed, sometimes slightly rimose, numerous, crowded to fused (2-4), rarely scattered, c. 0.7-2.0 mm in diam.; ostioles: 1-5 per verruca, hyaline to brown or black, sometimes surrounded by a white border, sunken, grouped in a central depression, rarely papillate, c. 0.05-0.14 (-0.24) mm wide Apothecia: 2-5 per verruca, fruit center hyaline to pink; epithecium: hyaline; hypothecium: hyaline asci: cylindrical to subclavate, 285-415 x 40-49 µm, 4-8-spored, uniseriate to biseriate ascospores: hyaline, ellipsoid to fusiform, 55-110 x 22-42 µm; spore walls: smooth, c. 5-10 µm thick, thickened at apices, 2-layered; outer spore wall: c. 1 µm thick; inner spore wall: 4-9 µm thick Pycnidia: not seen Spot tests: K-, C-, KC-, P-, UV+ gray Secondary metabolites: 2'-O-methylperlatolic acid and 4,5-dichlorolichexanthone (both major), 2'-O-methylisohyperlatolic and 2'-O-methylsuperlatolic acids (both minor). Substrate and ecology: on bark of Pinus and Quercus World distribution: described from Sri Lanka and also occurs in western North America Sonoran distribution: mountainous areas of Sonora, Chihuahua and Baja California Sur at 1500-2320 m. Notes: Pertusaria mesotropa is characterized by the 4-8-spored asci, the ellipsoid to fusiform ascospores and the presence of 2'-O-methylperlatolic acid and 4,5-dichlorolichexanthone. The species is very similar to the Australian P. paragibberosa Archer described recently (Archer 1991) and the distinction of the two species should be re-examined.