Life habit: lichenized, lichenicolous or not Thallus: squamulose squamules: up to 3 mm diam., scattered to adjacent, rounded or irregular to weakly elongated, plane to moderately convex upper surface: white, entirely covered by farinose to granulose pruina, dull, smooth, lacking pores and pseudocyphellae upper cortex: up to 30 µm high, containing calcium oxalate margin: concolorous with upper surface Apothecia: up to 2 mm diam., ± plane and marginate, sometimes becoming convex and immarginate, faintly to densely pruinose; exciple: dark reddish brown in the rim, paler in inner part; hypothecium: pale brown to colorless; epithecium: reddish brown (K+ red, N-) asci: clavate, 8-spored ascospores: bacilliform to acicular, (1-) 3 septate, 29-37 x 2.5-3.5 µm Pycnidia: laminal, immersed conidia: filiform Spot tests: all negative Secondary metabolites: none detected. Host: cyanolichens Substrate and ecology: on acidic rock on steep to overhanging rock wall in Madrean oak-pine forest at 1800 m World distribution: Mexico (Chihuahua and Oaxaca) and South America (Argentina, Peru, and Venezuela) Sonoran distribution: Chihuahua (single locality in Barranca del Cobre). Notes: The spores are unusually long in the Chihuahuan specimen. Based on measurement of 65 spores in material from Oaxaca and South America, Timdal (1991) described the spores as narrowly ellipsoid to bacilliform, 16.5-26.5 x 3.5-5 µm. South American material sometimes contain terpenoids. The species is morphologically quite similar to T. subdiffracta; they differ mainly in the pigments in the apothecium, in spore shape, and in secondary chemistry.