Thallus: areolate to rimose-areolate, with thin to moderately thick verrucae; margins: entire, often zoned upper surface: gray to pale gray, smooth, dull, epruinose; lacking soredia isidia: granular to papillate, 0.12-0.24 mm diam., 0.73-1.2 mm tall, with browned tips, numerous, scattered fertile verrucae: creamish, pertusariate, globose to hemispherical, smooth, sessile, numerous, scattered to crowded, 0.7-1.3 mm diam.; ostioles: 1-8 per verruca, hyaline, rarely dark, 0.02-0.1 (-0.2) mm diam. Apothecia: 1-2 per verruca, fruit center hyaline to pale brown; epithecium: brown; hypothecium: hyaline asci: cylindrical to clavate, c. 260 x 50-85 µm, 2-spored ascospores: uniseriate, hyaline, ellipsoid, 90-130 x 42-61 µm, 2-layered; spore wall: 2-layered; outer spore wall: 3.0-7.0 µm thick, smooth; inner spore wall: generally multilayered, 8.5-10.5 µm thick Pycnidia: not seen Spot tests: K+ yellow to red, C-, KC-, P+ yellow to orange, UV- Secondary metabolites: norstictic acid (major), connorstictic and subnorstictic acids (both minor). Substrate and ecology: siliceous rocks, such as basalt or schist, at 900-2100 m World distribution: western North America and western Europe and the Canary Islands disjunct; common in temperate and Mediterranean Europe, restricted to the southwestern part in North America Sonoran distribution: mountainous areas of Chihuahua, Sonora, and Baja California Sur. Notes: Pertusaria pseudocorallina is characterized by the presence of verrucose to papillate isidia with darkened tips which leave crater-like hollows on the thallus when broken off. The thallus contains norstictic acid. While most specimens, if not all, in Europe are sterile (cf. Erichsen 1936), the North American material is usually richly fertile. The verrucae are pertusariate and the asci contain two ellipsoid ascospores. No other Pertusaria species in the area has isidia and it is therefore easily recognized. Other Pertusaria taxa with isidia in North America include species with disciform apothecia, such as P. bryontha (Ach.) Nyl. or P. oculata (Dicks) Th. Fr., which are hardly confused with P. pseudocorallina, since these are more or less arctic-alpine species occurring on soil or mosses. The only other Pertusaria species with poriform ascomata and isidia in North America is P. globularis (Ach.) Tuck., but this taxon is easily separated by sorediate isidia and the presence of 2'-O-methylperlatolic acid and 4,5-dichlorolichexanthone.