Life Habit: lichenized, probably lichenicolous Thallus: squamulose squamules: up to 3 mm diam., adjacent, rounded to irregular, moderately convex upper surface: pale yellowish gray, epruinose, dull, smooth, lacking pores and pseudocyphellae upper cortex: up to 20 µm high, containing crystals dissolving in K, lacking calcium oxalate margin: concolorous with upper surface Apothecia: up to 1 mm diam., plane to weakly convex, with a narrow, indistinct margin, faintly pruinose; exciple: dark brown in the rim, paler in inner part; hypothecium: olivaceous brown in upper part, dark brown in lower part; epithecium: pale olivaceous brown (K-, N-) to colorless, containing crystals dissolving in K asci: clavate, 8-spored ascospores: narrowly ellipsoid, simple or 1-septate, 12-15.5 x 3.5-4.5 µm Pycnidia: not seen Secondary metabolites: gyrophoric acid, usnic acid, undetermined terpenoids. Host: probably cyanolichens Substrate and ecology: on rock in open oak forest at 1400 m World and Sonoran distribution: Baja California Sur (single locality). Notes: Within Toninia, the species shows several unique characters: a pale olivaceous brown (K-, N-) to colorless epithecium, presence of crystals dissolving in K in the epithecium, and presence of gyrophoric acid and usnic acid in the thallus. There are no apparently closely related species, and it is difficult to place it in any of the informal subgroups of Toninia proposed by Timdal (1991). In the two other yellow species of Toninia, T. gobica Golubk. (Mongolia) and T. sculpturata, the pigment is a cell wall pigment which is insolvable in acetone.