Life habit: lichenized Thallus: crustose, areolate, without elongated lobes; prothallus: present, black surface: gray or white, smooth or pruinose, without asexual propagules cortex: cellular Apothecia: adnate, 0.3-1 mm in diam., lecanorine disc: dark brown or black, flat, epruinose or pruinose margin: persistent, flush; thalline margin present, concolorous with thallus; proper margin not visible parathecium: elongate to oval cells; exciple below hypothecium irregular hyphae epihymenium: light brown or gray, K+ violet, cN+ violet hymenium: hyaline, 85115 µm tall paraphyses: 1-2 tip cells slightly swollen, not branched or with few branches; subhymenium hyaline asci: cylindrical, 8-spored ascospores: hyaline, 2 locules, ellipsoid, 12.5-15.5(-17) x 7-8.5(-9.5) µm, isthmus 3-3.5(-4) µm, spore end wall thin Pycnidia: not observed Spot tests: apothecial margin K+ violet, cN+ violet; thallus K+ violet, cN+ violet Secondary metabolites: thalloidima green. Substrate and ecology: on calcareous rocks World distribution: Europe and North America Sonoran distribution: Arizona. Notes: Caloplaca variabilis is usually strongly white pruinose with light gray areolate thallus. The epihymenium and thallus are K+ violet (in a section on a slide). It looks very much like a member of the Lecanora dispersa group but the spores easily separate these. Caloplaca atroalba is not pruinose and has a narrower spore isthmus.