Thallus: rimose-areolate or continuous to rimose, with thin to moderately thick verrucae; margins: entire, unzoned upper surface: whitish gray to greenish gray, smooth, shiny or dull, epruinose; lacking soredia or isidia fertile verrucae: concolorous with thallus, pertusariate or erect, flat-topped, numerous, often fused, c. 0.6-2.0 mm in diam.; ostioles: 1-6 per verruca, slightly sunken, grouped in a central depression, c. 0.1-0.5 mm wide, dark brown, whitish gray pruinose Apothecia: 1-4 per verruca, up to 0.7 mm in diam.; epithecium: dark brown, K -; hypothecium: hyaline asci: cylindrical, 320-400 x 52-75 µm, 6-8-spored, uniseriate ascospores: hyaline, broadly ellipsoid to ellipsoid, 75-110 x 36-58µm; spore walls: smooth, c. 8-12 µm thick, apices up to 20 µm thick, 2-layered; outer spore wall: c. 1-2 µm thick; inner spore wall: 7-11 µm thick Pycnidia: not seen Spot tests: K-, C-, KC-, P-, UV+ yellow Secondary metabolites: lichexanthone and 2-O-methylperlatolic acid (both major), planaic acid (minor). Substrate and ecology: Pertusaria mariae grows on siliceous rocks in open situations. A few specimens were also collected on soil World distribution: endemic to North America Sonoran distribution: in mountainous areas of southern Arizona, Sonoran and Chihuahua at 500 -2000 m. Notes: Pertusaria mariae is characterized by the whitish gray, rimose-areolate thallus, the pertusariate to erect verrucae with numerous non-fusing ostioles, the 6-8-spored asci and the presence of lichexanthone (UV + yellow) and 2-O-methylperlatolic acid. It is similar to P. tejocotensis which can be distinguished chemically by the presence of thiophaninic acid (UV + orange) and confluentic and planaic acids. Morphologically P. tejocotensis differs in having a yellowish thallus. Another similar species is P. wulfenoides which seldom occurs on rocks, but differs chemically (norstictic and thiophaninic acids) and morphologically (thallus yellowish, ostioles fusing). Another saxicolous species containing lichexanthone is P. moreliensis, which can be readily distinguished by the sorediate thallus.