Life habit: saprobic, not lichenized Thallus: sterile mycelium immersed in the substrate, infested area often paler than surrounding wood Apothecia: black or brownish black, 0.5-0.9 mm tall capitulum: 0.2-0.3 mm in diam., obconical to lenticular, with convex upper surface exciple: poorly to very well developed, 15-50 µm thick; when thin consisting of a few layers of narrow, periclinally arranged, heavily sclerotinized hyphae; when better developed of intricately intertwined, pale to slightly brown hyphae with swollen walls or of rows of pale brown, short cylindrical cells with only moderately thickened walls stalk: epruinose, consisting of periclinally arranged, sparsely intertwined and branched, dark to dark greenish brown hyphae, c. 3 µm in diam., with stalk hyphae ±more brown or reddish brown towards the surface of the stalk, K- or K+ slightly reddish-brown, HNO3 or slightly intensified reddish brown hymenium: dark brown above, 50-85 µm tall; hypothecium: dark brown, broadly obconical, 60-90 µm thick asci: 39-42 x 3-3.5 µm, cylindrical, with uniseriately arranged spores; apical part strongly and uniformly thickened and without canal, also in semi-mature asci ascospores: dark brown, simple, broadly ellipsoidal to ellipsoidal, slightly fusiform and flattened, 7-8 x 3.5-4 µm, without surficial ornamentation or faint and irregular under the light microscope Pycnidia: not very frequent, but when occurring often numerous, black, spherical to somewhat ovoid, often with a distinctively extended apical part, 0.15-0.20 mm in diam., with distinct apical pore; conidiogenous cells: narrowly cylindrical to lageniform, 9-11 x 1 µm conidia: 4-5 x 1-1.5 µm Secondary metabolites: none detected, although a red pigment is sometimes present in the apothecia and is formed abundantly in axenic cultures. Substrate and ecology: on dry, weathered wood and worked timber, particularly of Pinus, also common on wood of Picea and on lignum of deciduous trees (e.g., Salix), rarely on bark, in open situations World distribution: widely distributed, temperate to boreal in Eurasia, North America (Alaska, Mexico), Central America, South America, and Australasia Sonoran distribution: Arizona, southern California, and Baja California Sur. Notes: Mycocalicium subtile is characterized by having a stalk consisting of periclinally arranged, dark hyphae, and by having dark brown, flattened fusiform non-septate spores and an ascus with a thick apex without canal. It differs from M. albonigrum in its exciple and ascus apex structure; see under that species. Chaenothecopsis nana is easily mistaken for Mycocalicium subtile, and the ascus tip should always be checked; that in M. subtile is strongly thickened and without a visible canal in semi-mature and mature stages. Mycocalicium subtile also has larger asci and the spores are longitudinally arranged in the asci or occasionally slightly irregularly oriented, but never as densely and obliquely stacked as in C. nana. Mycocalicium subtile seems to occur exclusively on lignum, and preferably in rather dry and open situations. Chaenothecopsis nana, however, occurs on the bark of conifers (or rarely on that of deciduous trees), and also the lignum of conifers; it occurs in rather humid situations, often 1-3 m above the ground, on trunks. See Tibell (1990, 1998 & 1999) for fuller description.