Life habit: not lichenized or lichenized Thallus: mycelial, disrupting the hosts bark and giving it a pale appearance photobiont: absent Ascomata: ±round to ellipsoid, 0.2-0.5 µm in diam., immersed to erumpent, up to 100 µm thick epihymenium: reddish brown, 10-20 µm thick hymenium: hyaline, 30-60 µm tall; paraphysoids: hyaline, with hyphae 1-1.5 µm wide, in a gel with granules; sub-hymenium: hyaline, 5-10 µm thick asci: subglobose, with distinct stipe, with laterally thickened walls, 35-55 x 30-45 µm, 8-spored ascospores: persistently hyaline, 1-septate (not incised at septum), broadly ovoid, 17-21 x 9-12 µm, without an epispore Pycnidia: up to 0.1 mm wide, unilocular conidia: bacilliform, 3-5 x 1 µm Chemical reactions: ascomatal gels I+ red, KI+ blue; ascus tholus KI+ faintly blue but ring-structure inconspicuous. Substrate and ecology: the species is known from young and exposed branchlets, and seems to be a pioneer species on smooth bark. In the Mediterranean it is common in the littoral zone World distribution: Mediterranean region of Europe and North America (California) Sonoran distribution: southern California (Santa Monica Mts). Notes: Arthonia granosa is easy to recognize by its unusual broad ascospores and its subglobose asci, which reminds one of species assigned to Arthothelium. Externally, it resembles Arthonia galactites and similar species. Redinger (1937) mentioned the occasional presence of Trentepohlia as a photobiont.