Thallus: crustose, effuse, rimose-areolate with smooth surface, in section up to 1 mm thick, prothallus: thin, smooth, dark brown surface: creamy, white or pale brown cortex: up to 40 µm thick, mainly composed of intertwined slightly brownish hyphae medulla: white, variable in thickness, composed of loosely interwoven hyphae with many crystals of unknown nature (soluble in K) Apothecia: immersed to adnate, lirellate, lirellae: simple or slightly branched, straight to curved, scattered, rarely 2-3 aggregated, 0.7-2 x 0.3-0.7 mm disc: narrow, slit-like margin: black, thick, entire; excipular lips: often with thin layer of white pruina exciple: thick, brown and carbonized laterally, rarely extending to the base, carbonized part not well separated from a paler yellow to hyaline cover and the lateral thalline margin epihymenium: not present hymenium: hyaline, not inspersed, 100-120 µm tall, I-, K/I-; paraphyses: up to 2.5 µm thick, septate, slightly branched, tips hyaline, not thickened; periphysoids: periphysoid-like hyaline hyphae with smooth surface covering the apices of the carbonized lips; subhymenium: well developed, hyaline to pale yellow, 50-120 µm thick asci: clavate, 90-110 x 16-20 µm, 8-spored, with uniseriate ascospores when young ascospores: hyaline, transversely 4-7-septate, oblong ellipsoid to fusiform, 21-28 x 8-11 µm, I- Pycnidia and conidia: not found Spot tests: cortex and medulla K+ yellow turning orange-red, C-, KC-, P+ orange Secondary metabolites: norstictic and connorstictic acids. Substrate and ecology: on volcanic rock, that are moderately shaded, usually north-facing, vertical or almost vertical and on underhangs World and Sonoran distribution: coastal areas of southern California and Baja California (probably endemic). Notes: "Graphis" saxorum differs from all other Graphis species (sensu Staiger 2002) by its I- reaction of the ascospores and the presence of periphysoid-like hyphae, that indicate a closer relationship with the genus Carbacanthographis (Staiger 2002). However, in that genus the periphysoids have a warty surface and the paraphyses are much thinner (at most 1.5 µm wide). Probably this species belongs in a new undescribed genus, but molecular data should be sought before a final decision is made.