Life habit: lichenized Thallus: little or none, crustose, without elongated lobes; prothallus: absent surface: gray, smooth, without asexual propagules cortex: indistinct Apothecia: adnate, 0.3-0.7 mm in diam., lecanorine disc: dark reddish orange, flat, epruinose margin: persistent, flush to slightly raised; thalline margin absent; proper margin visible, little lighter than disc parathecium: elongate to oval cells hymenium: hyaline, 55-70 µm tall paraphyses: 1-2 tip cells slightly swollen, with few or with some branching; subhymenium hyaline asci: cylindrical, 8-spored ascospores: hyaline, 2 locules, ellipsoid, 11-12.5(-17) x 4-5.5 µm, isthmus 1-1.5(-3) µm, spore end wall thin Pycnidia: not observed Spot tests: apothecial margin K+ red Secondary metabolites: parietin, fallacinal, emodin, and teloschistin. Substrate and ecology: on non-calcareous rocks World distribution: worldwide Sonoran distribution: southern California, Arizona, Baja California, and Baja California Sur. Notes: Caloplaca arenaria has little or no visible thallus, flat apothecia that are usually somewhat angular and occurs on non-calcareous rocks. Caloplaca marmorata has convex apothecia and occurs on calcareous rocks. Caloplaca luteominia var. bolanderi has flat to slightly convex red-brown apothecia, more thallus, and has larger spores.