Life habit: saprobic, not lichenized Thallus: sterile mycelium immersed in the substrate, sometimes rendering it a whitish color Apothecia: black, brown-black, 0.5-0.8 mm tall, all parts of the apothecia K-, N- capitulum: 0.2-0.4 mm in diam., obconical to lenticular, with convex upper surface, the disc convex, brownish black exciple: dark brown, usually well developed, 20-45 µm thick, consisting of large, 7-12 µm wide, almost isodiametric, thin-walled cells in 2-4 layers; innermost hyphae of the exciple not swollen, continuous with the hyphae of the upper part of the stalk stalk: 0.10-0.15 mm in diam., epruinose, shining black, consisting of dark brown, parallel hyphae, c. 3 µm in diam. hymenium: dark brown above, 50-60 µm tall; hypothecium: broadly obconical, dark brown, 140-170 µm thick asci: cylindrical, 35-45 x 3-4 µm, with uniseriately arranged spores, with apical part of semi-mature asci thickened and with a short and wide canal, and finally mature asci uniformly thickened, ascospores: blackish brown, simple, broadly ellipsoid to oblong-ellipsoid, slightly fusiform and flattened, 6-8.5 x 3-4 µm, without ornamentation of the surface or faint and irregular under light microscope Pycnidia: not very frequent, but sometimes numerous, black, spherical to ovoid or pyriform, often with a distinctively extended apical part, 0.10-0.20 mm in diam., with distinct apical pore; conidiogenous cells cylindrical to irregular with a ±swollen base, 7-8 x 1.5-2 µm conidia: 4-5 x 1.5-2 µm Secondary metabolites: none detected. Substrate and ecology: on dry, hard, weathered wood; on bark, especially oaks World distribution: North America (New England, New York, Alabama, Texas, California, and Mexico), Central America, South America and Australasia Sonoran distribution: Arizona and Baja California Sur. Notes: Mycocalicium albonigrum is characterized by having non-septate fusiform spores and an exciple consisting of very large and thin-walled cells. It is very similar to M. subtile, but differs in its exciple structure. The two species also differ in ultrastructural details of conidiophores and conidia and culture characteristics. See Tibell (1982), Tibell (1990), and Vinuesa et al. (2001) for more information.