Thallus: absent or immersed in the substrate, upper surface: grayish photobiont: absent Perithecia: hemispherical, ± circular in outline, unilocular, black, semi-immersed in the bark, 0.1-0.2 mm diam. ascomatal wall: black, absent below the hamathecium hamathecium: pseudoparenchymatic tissue, lacking filaments, not inspersed with oil droplets asci: globose, c. 17-25 µm diam., 40-45 µm tall, with 8, irregularly arranged ascospores ascospores: hyaline, clavate, 3-septate (starting with a median euseptum), becoming submuriform, 14-15 x 5-6 µm; walls: not ornamented, without a gelatinous sheath Spot tests: all negative, UV negative Secondary metabolites: none detected. Substrate and ecology: on bark of Quercus (in Europe often on Aesculus) World distribution: temperate in the Northern Hemisphere Sonoran distribution: only collected in southern Arizona, on Quercus. Notes: The distantly related Mycoporum compositum (A. Massal.) R. C. Harris has been erroneously reported from the area; it has a filamentous hamathecium and is lichenized. It may be confused with Arthopyrenia species that have 1 (-3)-septate spores.