Life habit: lichenized Thallus: immersed, crustose; prothallus: absent; without asexual propagules Apothecia: adnate, 0.3-0.8 mm in diam., lecanorine disc: reddish brown, flat or convex, epruinose margin: persistent or disappearing, flush; thalline margin absent; proper margin not visible or visible, concolorous with disc parathecium: irregular hyphae, exciple below hypothecium amorphous epihymenium: golden, K+ red, C- hymenium: hyaline, 70-85 µm tall paraphyses: 1-2 tip cells slightly swollen, with few branches; subhymenium hyaline asci: cylindrical, 8-spored ascospores: hyaline, 2 locules, ellipsoid, (12.5-)14-15.5 x 4-5.5 µm, isthmus 1.5-3 µm, spore end wall thin Pycnidia: not observed Secondary metabolites: parietin, fallacinal, emodin, and teloschistin. Substrate and ecology: in calcareous rocks World distribution: Europe and North America Sonoran distribution: southern California and Baja California Sur. Notes: Caloplaca marmorata is a member of the C. lac-tea group with immersed thallus growing on calcareous rock, narrow spore isthmus, and dark brown-red convex apothecia. The only other similar species is C. luteominia var. bolanderi but that has larger apothecia and usually has more visible thallus. Caloplaca arenaria has flat apothecia and occurs on non-calcareous rock.