Thallus: crustose, episubstratic, thick, off-white to pale fawn surface: smooth, somewhat shiny, usually distinctly verruculose true cortex: lacking but covered by epinecral layer medulla: filled with large crystals Ascomata: orbicular to slightly elongated, initially perithecioid, later expanding and appearing almost apothecioid; solitary, distinctly emergent, subglobose to urceolate, 0.5-1.2 mm in diam. pore: round to elongate, ±entire margins: concolorous with thallus to dark gray at maturity, apically often erroded and pruinose with age true exciple: carbonized, entire hypothecium: partly to entirely carbonized hymenium: hyaline, not inspersed, up to 350 µm tall, with non-amyloid hymenial gel paraphyses: simple to slightly branched, without distinct apical thickening asci: subcylindrical, 1-2-spored ascospores: hyaline, slightly yellow when old, densely muriform, oblong to fusiform, amyloid, 100-250 x 20-45 µm Pycnidia: not observed Secondary metabolites: none detected. Substrate and ecology: on bryophytes or on bark (e.g., Quercus), predominantly in tropical montane (rain)forests in elevations ranging from 1100 to 2000 m World distribution: Neotropical Sonoran distribution: Sinaloa at 1700 m, presently known only from one collection. Notes: This species is characterized by its emergent ascomata with large ascospores, 1-2-spored asci, and the lack of secondary metabolites. It is similar to "Thelotrema" isidatum Hale (Hale 1975), described from Venezuela. This taxon may be conspecific with G. mexicana, but we have not been able to study the type. Morphologically, the species is similar to Pertusaria species, but is readily distinguished by its muriform ascospores. In contrast to Hale (1974), we found the true exciple in Sonoran material and the type being distinctly carbonized.