Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Life habit: lichenized Thallus: crustose, areolate, without elongated lobes; prothallus: present or absent, black surface: dark gray to brownish-gray, smooth, without asexual propagules cortex: indistinct, thin Apothecia: adnate, 0.3-0.6 mm in diam., lecanorine disc: dark reddish orange or orange, flat, epruinose margin: persistent, raised; thalline margin present or absent, concolorous with thallus; proper margin visible, little lighter than disc parathecium: consisting of radiating hyphae or elongate to oval cells; exciple below hypothecium amorphous epihymenium: golden, K+ red or K+ violet, H-, 10%N + violet, cN-, C- or C+ red hymenium: hyaline, 50-70 µm tall paraphyses: 2-3 tip cells slightly swollen, with few branches or with some branching; subhymenium hyaline asci: cylindrical, 8-spored ascospores: hyaline, 2 locules, ellipsoid, 11-17 x 5.5-8.5 µm, isthmus 4-5.5 µm, spore end wall thin Pycnidia: not observed Spot tests: apothecial margin K+ red, H-, 10% N-, cN-, C-; thallus K- or K+ violet, H+ violet, 10%N+ violet, cN+ violet, C- Secondary metabolites: unidentified anthraquinones and thalloidima green. Substrate and ecology: on non-calcareous rocks World distribution: Europe, western North America Sonoran distribution: southern California, Arizona, Baja California, western Chihuahua, and Sonora. Notes: Caloplaca atroflava has a thin gray to brownish gray areolate thallus and dark orange apothecia with orange margins that are characteristic of this species. On the older apothecia there is often a little gray thalline margin. The proper margin usually reacts C+ red-brown and often the epihymenium has a K+ red to violet reaction. The thallus is typically dark gray to light brownish and reacts K+ violet but on some specimens the thallus is lighter gray and the K reaction is negative. Caloplaca sonorae is similar but has a subsquamulose thallus. Caloplaca sideritis has a dark excipular ring in the margin.