Thallus: crustose to small squamulose or almost placodioid, granular, 0.5-2 mm wide lobes: poorly developed, 0.05-0.1 mm wide and long, 50-100 µm thick surface: brown to blackish brown, smooth, convex, not isidiate internal anatomy: with upper and lower cortices consisting of irregularly isodiametrical cells., internally not paraplectenchymatous and with loosely interwoven chains of Nostoc Apothecia: common, laminal, sessile, (0.2-)0.4-1 mm wide disc: blackish brown, prominent, concave to plane margin: not thalline exciple: well developed hymenium: hyaline below and thinly brown above, 70-90 µm tall asci: cylindrico-clavate, 8-spored ascospores: hyaline, submuriform, (23-)25-30 x (8-)11-14 µm Pycnidia: not observed Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: on rocks, usually calcareous ones World distribution: Europe and tentatively North America Sonoran distribution: southern California (Hasse Ex. 94). Notes: Leptogium biatorinum is a variable species, in which the lobes can vary from granular to flabellate, a variation which appears to be environmentally controlled. In North America there is only one specimen which is also rather similar to the poorly understood L. parculum Nyl. that is totally crustose, has smaller spores and grows at the Arctic coasts of Alaska. In Europe L. biatorinum has been confused with L. byssinum (Hoffm.) Zwackh ex Nyl., but that species is more crustose and granular and has sunken apothecia (see photos in Jørgensen 1994).