Thallus: verruculose, often forming round patches up to 10 cm wide verruculae: 0.5-2 mm wide, c. 1 mm high, contiguous; rim: not distinct upper surface: whitish brown to dark brown, dull, convex, sometimes fissured, usually pruinose with distinct patch at apex becoming ring around apothecium cortex: paraplectenchymatous, eucortex: thin, c. 20 µm thick, indistinct, with a brownish upper pigmentation zone algal layer: ±50 µm, algal cells to 10 µm wide medulla: white, continuous, with attaching plectenchyma attachment: broad Apothecia: one per squamule, round, immersed; sometimes appearing to have more than one apothecium per squamule when in process of asexual division of thallus; punctiform, but occasionally expanding disc: dull brown, plane, round, usually large-flaked pruina forming a ring around disc, verrucae often fissured when disc is fully expanded parathecium: distinct, thickness c. 25 µm or less epihymenium: dark brown, c. 10 µm thick hymenium: hyaline, ±120µm tall; paraphyses: thick and spreading in water, c. 1.7 µm wide at base, with coherent and not expanded apices subhymenium: pale yellow, 40-50 µm thick; hypothecium: 10-20 µm thick asci: saccate, usually high as hymenium, width depending on amount of spores, 8, 16-24-48(-100?)-spored ascospores: hyaline, simple, globose, (9-)10-13(-15) µm in diam. Spot tests: UV-, all spot tests negative Secondary metabolites: none detected. Substrate and ecology: on soil, often derived from granite Sonoran distribution: southern California and Baja California, inland to elevation of 930 meters and apparently from San Benito County (Pinnacles National Monument) south, not yet collected on Channel Islands. Notes: Acarospora thelococcoides is an indicator of undisturbed soil habitats and often occurs at sites of the rare and endangered Quino Checkerspot Butterfly and Texosporium sancti-jacobi.