Life habit: lichenized Thallus: bullate areolate to squamulose, pale greenish brown to brown areoles: 0.2-0.6 mm wide and 0.2-0.5 mm thick, algae present almost to the areole's base, but usually lacking in the upper 25-40 µm, where dead algal cell walls are pushed towards the upper surface in a phenocortex composed of pale to brownish pigmented hyphae photobiont: Trebouxia; cells: 9-15 µm diam. Ascomata: black, dispersed, ±round, convex, up to 2.5 mm in diam., isolated to confluent, emerging from the margin of the areoles epihymenium: olive-brown, 15-20 µm thick, with paraphysoidal tips up to 3.4 µm wide and apically bent sidewards and then collapsing, apparently not anastomosing hymenium: hyaline, c. 50 µm tall; paraphysoids: anastomosing, 2-3 µm thick; subhymenium: dark brown, 100-400 µm thick asci: clavate, 40-50 x 10-15 µm, 8-spored ascospores: hyaline, 1-septate, obovate, 10-14 x 4-6 µm, with a gelatinous epispore Pycnidia: not observed Chemical reactions: ascomatal gels I+ red, KI+ blue; ascus tholus KI-. Substrate and ecology: on soil World distribution: North America and the Himalayas Sonoran distribution: southern California (Riverside Co. and Santa Cruz Island). Notes: Egea and Torrente (1995) suggested excluding Arthonia glebosa from Arthonia because of its unusual characters within Arthonia, i.e. its thickish thallus, which is similar to Toninia spp., and its slightly different ascus shapes. In fact, this species seems not related to Arthonia s. str. Some morphotypes of Arthonia lapidicola can resemble a tiny Arthonia glebosa. However, there are no clear-cut differences in ascomatal construction that could clearly separate A. glebosa from other Arthonia species associated with green algae (including species parasitic on hosts with such algae as photobionts). Arthonia terrigena, another species on soil in North America and also having 1-septate ascospores, is readily distinguished by its inconspicuous thallus and its paler subhymenium.