Thallus: black, crustose to squamulose, areoles/squamules small, 0.5-1 mm wide, ± angular or roundish in outline, not rosette-shaped, surface: black, rough, attachment: by a central bundle of rhizohyphae Apothecia: sessile, zeorine, 1-3 (-5) per squamule, c. 0.5 mm wide; disc: dark red, slightly depressed, open; thalline margin: persisting, smooth; exciple: 10-20 µm thick, hyaline, composed of loosely interwoven thin hyphae; epihymenium: faintly yellowish-brown; hymenium: hyaline, amyloid, up to 125 µm high; paraphyses: distinctly septate, sparingly branched and anastomosing; apical cells: c. 3 µm thick; hypothecium: c. 12.5 µm thick asci: 8-spored ascospores: simple, hyaline, globose to broad ellipsoid, 7.5-10 x 7.5 µm; walls: thin; in old, deformed spores c. 2.5 µm wide Pycnidia: immersed, simple, globose, c. 0.1 mm wide conidia: small, bacilliform or ellipsoid, c. 3 x 1 µm Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on limestone, on sheltered, steep or exposed faces of boulders on rocky slopes; chaparral woodlands and pine-oak forests World distribution: southern Europe, NW Africa and SW North America Sonoran distribution: limestone deposits in central Arizona. Notes: This is the smallest species of the genus with an almost crustose-areolate growth form. Similar genera are Psorotichia and Porocyphus, both of which have a paraplectenchymatous anatomy composed of smaller cells. Phloeopeccania is similar in anatomy but either has polysporous asci or large apothecia with thick (c. 125 µm), prominent thalline margins, depressed to urceolate discs, no exciple and a different type of ascoma ontogeny (groups of coiled ascogonia). Gloeoheppia polyspora differs in the subgelatinous thallus with cavities, the dark brownish thallus color, and polysporous asci.