Thallus: squamulose squamules: dispersed or slightly overlapping to imbricate, loosely attached, divided surface: with medullary hyphae merging into the blackish-brown rhizohyphal web upper surface: grayish or greenish brown, often with spotty pruina (mostly on distal parts of the lobes) medulla: composed of ± loose hyphae with many spherical cells and distinct interhyphal spaces lower cortex: lacking Perithecia: pyriform; walls: hyaline or pale yellowish-brown except for the dark ostiole; periphyses: rather short (up to 30 micro meter long), often with somewhat swollen (-5 micro meter in diam.) apical cells asci: clavate, 55-65 x 13-16 micro meter, 8-spored ascospores: elongate ellipsoid to subfusiform, c. 12-18 x 5-7 micro meter Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: mostly on bark and mosses in warm temperate sites World distribution: temperate Europe, East Africa, New Zealand, Japan, southwestern North America Sonoran distribution: known from several sites in central California, on oak (Quercus douglasii and Q. lobata) and from one site in southern Arizona on a mossy boulder and an oak. Notes: This species is the only bark-inhabiting species of Catapyrenium s.str. It is closely related to the terricolous and mainly arctic-alpine C. daedaleum (not known from the Sonoran area).