Life habit: lichenized Thallus: crustose, elongate lobed, margin abrupt at edge; with elongated lobes, 1-3 mm long, 0.4-1 mm wide; prothallus: absent surface: yellowish orange, smooth or shiny, without asexual propagules cortex: cellular, 7-35 µm thick, with granules insoluble in K; medulla dense, with granules dissolving in K Apothecia: adnate, 0.3-0.5 mm, lecanorine disc: red to orange, flat to convex, epruinose margin: persistent, flush; thalline margin present, concolorous with thallus; proper margin not visible parathecium: cellular (paraplectenchymatous); exciple below hypothecium amorphous epihymenium: golden, K+ red, H-, 10%N-, cN-, C- hymenium: hyaline, 70-85 µm tall paraphyses: 2-3 tip cells swollen, with some branching; subhymenium hyaline asci: cylindrical, 8-spored ascospores: hyaline, 2 locules, ellipsoid, 10-15 x 6.5-7 µm, isthmus 5.5-7 µm, spore end wall thin Pycnidia: present, mostly immersed, ostiole orange Spot tests: apothecial margin K+ red, 10% N-, cN-; thallus K+ red, 10%N-, cN-; medulla IKI- Secondary metabolites: unidentified anthraquinones. Substrate and ecology: on non-calcareous rocks World distribution: Northern Mexico Sonoran distribution: Baja California Sur, Sonora and northern Sinaloa. Notes: Caloplaca appressa is a variable species with broadening and appressed lobe tips, the central portions with convex areoles, and with usually reddish apothecia. The spore isthmus is also wider that similar species. The isthmus is usually at least as long as the spore width. Caloplaca appressa is similar to C. saxicola and C. impolita but differs from the former mainly in the more yellowish, orange flattened, appressed lobes and from the latter by geographical distribution.