Life habit: lichenized Thallus: crustose, areolate, without elongated lobes; prothallus: absent surface: gray, verruculose, without asexual propagules cortex: cellular, 7-30 µm thick, granules absent; medulla without granules Apothecia: adnate, 0.2-0.8 mm in diam., lecanorine disc: orange, flat or convex, epruinose margin: persistent, slightly raised; thalline margin present, concolorous with thallus; proper margin visible, dark brown to black parathecium: cellular (paraplectenchymatous), exciple below hypothecium amorphous epihymenium: golden, K+ red, H-, 10%N-, cN-, C- hymenium: hyaline, 55-70 µm tall paraphyses: 1-3 tip cells swollen, with few branches; subhymenium hyaline asci: cylindrical, 8-spored ascospores: hyaline, 2 locules, ellipsoid, 11-14 x 5.5-7 µm, isthmus 3-4 µm, spore end wall thin Pycnidia: present, totally immersed, ostiole black Spot tests: apothecial margin K+ violet, H+ violet, 10% N+ violet, cN+ violet, C+ violet; thallus K+ violet, H+ violet, 10%N+ violet, cN+ violet, C+ violet Secondary metabolites: unidentified anthraquinones and thalloidima green. Substrate and ecology: on non-calcareous rocks or occasionally on calcareous rocks World distribution: North America Sonoran distribution: Arizona. Notes: Caloplaca sideritis has a dark excipular ring around the disc of the apothecia (as seen under a dissecting microscope) and a light gray thallus. The thallus development is very variable and ranges from almost absent and thin to subsquamulose. The subsquamulose condition approaches C. pellodella and in some cases these two species are very difficult to distinguish but the thallus margins of C. sideritis are areolate. The radiating hyphae in the proper exciple are more developed in C. pellodella and C. sideritis has a much thinner cortex and necral layer with a rough surface. The rough necral layer never gives a shiny appearance to the thallus as is present in C. pellodella. Those collections with little thallus (usually on sandstone) approach C. exsecuta but that has no K+ violet parathecium and contains lecidea green.