Life habit: lichenized Thallus: crustose, continuous, without elongated lobes; prothallus: absent surface: gray, verruculose, without asexual propagules Apothecia: adnate, 0.3-1 mm, lecideine disc: brownish orange or brown, convex, epruinose margin: disappearing, flush; thalline margin absent; proper margin not visible or visible, concolorous with disc or little lighter than disc parathecium: consisting of radiating hyphae, exciple below hypothecium prosoplectenchymatous epihymenium: golden, K+ red, C+ violet hymenium: hyaline, 85-100 µm tall paraphyses: 1-2 tip cells slightly swollen, with few branches; sub-hymenium hyaline asci: cylindrical, 8-spored ascospores: hyaline, 2 locules, ellipsoid, 14-17(-18) x (7-)8.5-10 µm, isthmus 1.5-4 µm, spore end wall thickened Pycnidia: present, mostly immersed, ostiole black Spot tests: thallus K-, C- Secondary metabolites: unidentified anthraquinones, parietin, and emodin. Substrate and ecology: on bryophytes or detritus World distribution: Europe and North America Sonoran distribution: Arizona. Notes: Caloplaca sinapisperma is a muscicolous species with abundant light gray thallus and dark red-brown apothecia that lack a gray thalline margin. Caloplaca tetraspora has similar apothecia but has only four spores per ascus. Caloplaca ammiospila has apothecia with a gray thalline margin.