Thallus: chinky areolate stipe: composed of filamentous hyphae areoles: c. 1-2 mm broad, up to 0.7 mm high, basally ± constricted, slightly convex, separated by deep cracks, ± angular; marginal areoles: more roundish or slightly incised upper surface: grayish, lateral parts brown to blackish upper cortex: c. 15-25 µm thick, continuing laterally, composed of rounded-angular cells (5-9 µm diam.); epinecral layer: thin, causing the pruina medulla: subparaplectenchymatous, composed of cells 6-10 µm diam.; algal layer: 100-150 µm high; algal cells: 8-15 µm in diam. lower surface: brown to black; attached with a central stipe as a holdfast Perithecia: broadly pyriform to subglobose, up to 0.45 mm broad; wall: pale except for the ostiole, browning with age throughout; periphyses: 15-20 x 3-4 µm asci: clavate, 65-75 x 17-25 µm, 8-spored ascospores: simple, ellipsoid, 17-24 x 6-8 µm Pycnidia: immersed conidia: oblong-subcylindrical, 3-4 x 1 µm long Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on rock of different kinds (limestone, granite, sandstone, basalt) from low elevations to 1000 m, often among other crustose lichens, but not truly parasitic World distribution: SW North America in the mediterranean climate, northwards to Oregon Sonoran distribution: Arizona, southern California, Baja California and Baja California Sur. Notes: Within the genus the species is outstanding in its short and rather thickish periphyses. A specimen from Baja California has larger areoles (-4 mm), slightly broader spores (20-24 x 8-9 µm) often with an end attenuated, and larger conidia and may represent a separate species. Placopyrenium noxium has smaller thalli, smaller spores and longer conidia and is a constant parasite on Staurothele areolata. Dermatocarpon lorenzianum may be morphologically similar and has spores of almost equal size, but is easily separated by its prosoplectenchymatous medulla and a lower cortex of anticlinally arranged, strongly conglutinated hyphae.