Life habit: lichenized Thallus: coherent, granular or verrucose, soon compacted into a chinky crust, attached by the whole lower surface surface: white or pale gray cortex: 20-30 µm thick, hyaline, granular, composed of decaying photobiont cells and granular crystals forming a phenocortex photobiont: a chlorococcoid green alga; algal layer: 40-80 µm thick, continuous medulla: loose, gray, floccose; hyphae: strongly articulate, arranged "centrifugally" Apothecia: 0.5-0.8 mm in diam., about the same in height, cylindrical, lecanorine, sessile mazaedium: +protruded, black, olive-ochre-yellow to yellow-green pruinose thalline margin: with abundant light yellow or ochre-yellow pigment exciple: dark brown to black, in the upper part lined with yellow crystals on the surface, thick only at the base, with a network of brown hyphae reaching deep into the medulla of the thallus, thin above hymenium: paraphyses: forming a dense tissue, at first c. 2 µm wide, enclosing the spores like a halo, then becoming up to 6-8 µm wide with shorter and strongly pigmented cells asci: soon disintegrating, 38-48 x 4-5 µm, 8-spored ascospores: brown, 1-septate (but septum +obscured by the enclosing hyphae), rounded, obtuse at the poles, short-ellipsoid, with pseudoparenchymatous, many- and small-celled coat of enclosing hyphae (appearing highly "blistered"), (15-)19-26 x (7-)10-14 µm, including the hyphal coat (20-)35-44 x (16-)19-26(-30) µm; hyphal coat: pseudoparenchymatous, multi-celled, formed from the surrounding paraphyses; cells of hyphal coat: thin-walled and lobed-crenate, overlapping, the central cells highly vacuolated, with walls 1-2 µm thick Conidiomata: unknown Spot tests: thallus K-, C-, KC-, P- Secondary metabolites: containing calycin in the apothecial margin and in the mazaedium. Substrate and ecology: on soil and animal pellets (e.g. rabbit) World distribution: western North America, particularly arid intermountain areas Sonoran distribution: southern California. Notes: Texosporium sancti-jacobi is rather rare. It is easily distinguished from Cyphelium and Thelomma by the unusual spore structure (pseudoparenchymatous 'episporium').