Stromata to 1.5 mm diam, visible externally as a raised pustule to 0.75 mm diam, a black zone line completely enclosing or only beneath the perithecia is revealed on cutting into the substrate, a raised pustule is visible externally which splits at maturity to reveal an inconspicuous powdery white disc composed of hyaline crystals, a faint ridge may ring the pustule where the black zone meets the inner surface of the bark.
Ascomata perithecia, to 0.5 mm diam, mostly 6-8 per stroma, globose with long necks, ± upright, black, smooth, immersed beneath the bark in groups, necks united centrally and emerging through the white disc but not protruding beyond the substrate surface. Peridium 20-25 µm thick, composed of a layer of compressed dark brown-walled cells 8-10 µm thick at the exterior and an interior layer 12-15 µm thick of compressed hyaline cells. Interascal tissue absent, at least at maturity. Asci 166-173 x 12-14 µm, cylindrical, tapering to a rounded base, apex truncate, thick-walled, with two observable layers, J-, with a conspicuous refractive apical ring, 8-spored, arising in many fascicles over the entire inner surface of the ascoma. Ascospores 15-25 x 6-7 µm (excluding appendages), ellipsoidal, thick-walled with flattened thin-walled ends (appendage scars), hyaline, very faintly roughened, 1-septate, constricted at the septum, with one appendage at each end and 2 or 3 septal appendages each 6-12 µm long (best seen in water mounts or cotton blue in lactophenol) but sometimes missing.
Conidiomata to 1 mm diam, stromata 1-3 mm diam, pycnidial, separate or grouped, stromatic, blackish, composed of thick-walled angular cells. Conidiophores dichotomously or irregularly branched or whorled, septate, hyaline. Conidiogenous cells elongate, tapering, enteroblastic, phialidic, determinate, integrated. Conidia (5-)10-17 x 1-1.5 µm, elongate-cylindrical to filiform, strongly curved to sigmoid or ± straight, hyaline, simple, smooth.