Thallus: consisting of individual spherical verrucae, becoming inflated and lobed, 10-20 mm wide, attached to substrate by an umbilicus upper surface: light gray Apothecia: frequent, up to 2.5-3.5 mm in diam., at first immersed, becoming stipitate disc: black or slightly pruinose, persistently plane, cracked and sometimes regenerating following erosion margin: thalline, prominent concolorous with thallus epihymenium: red-brown with crystals included ascospores: brown 1-saptate, (12-)14.515.5(-18) x (6-)7.5-8.5(-9.5) µm; narrow torus visible in many spores Pycnidia: completely immersed in thallus, visible only as brown spots on surface, c. 0.35 mm in diam., ostioles brown to black conidia: hyaline, 2.5-3.5 x 1-1.5 µm long Spot tests: K+ yellow to red, C-, P+ yellow to orange Secondary metabolites: norstictic acid in medulla, atranorin in cortex and medulla. Substrate and ecology: on acidic rocks, basalt World distribution: southwestern coastal North America Sonoran distribution: southern California, Guadalupe Island, Baja California, Baja California Sur, above oceanic cliffs to 400 m. Notes: The morphology of the thallus is unique and gives the species a roccellaceous appearance. The massive thalline phenocortex with included dead algal cells and the irregular nature of its hyphae are very characteristic. Mobergia calculiformis is easily distinguished from M. angelica by the significantly smaller ascospores and their more strongly warted walls, thicker phenocortex, narrower conidia and different thalline morphologies. The lack of atranorin in M. angelica is also diagnostic.