Life habit: lichenized, not lichenicolous Thallus: granular to areolate areoles: up to 2 mm diam., irregular and often forming a ± continuous crust upper surface: grayish brown, ecorticate, scurfy, epruinose, dull, lacking pores and pseudocyphellae upper cortex: lacking margin: concolorous with upper surface Apothecia: up to 1 mm diam., remaining ± plane and marginate or plane and marginate when young, later convex and immarginate, epruinose; exciple: brownish black in the rim, reddish brown in inner part; hypothecium: reddish brown to dark brown; epithecium: medium brown, (K-, N-) asci: clavate, 8-spored ascospores: bacilliform, slightly curved, (3-) 7-septate, 24.5-34.5 x 3-4 µm Pycnidia: not seen Spot tests: all negative Secondary metabolites: none detected. Host: none Substrate and ecology: on sandstone in open habitat at the coast, at c. 180 m World and Sonoran distribution: California (San Miguel Island, single locality). Notes: Toninia nashii differs from the other crustose species of Toninia in having a medium brown, K-, N- epithecium and long, slightly curved, mainly 7-septate spores. Toninia mesoidea (Nyl.) Zahlbr. and T. philippea have a green, K-, N+ violet epithecium; the former more shortly bacilliform (13-17.5 x 5-6.5 µm), 3-septate spores, the latter ellipsoid, 1-septate spores. Toninia pennina (Schaer.) Gyelnik and T. weberi have a gray, K+ violet, N+ violet epithecium and ellipsoid, 1-septate spores. It is possible that the thallus described above belongs to a host lichen, not T. nashii. In that case, the most similar species would be T. subfuscae (Arnold) Timdal, which differs in having a greenish, K-, N+ violet epithecium and shorter (9.5-16 4-5.5 µm), 1- to 3-septate spores.