Anamorph: conidiomata intermixed with the ascomata, 150-200 µm diam. and 35-70 µm high, ± flat, opaque, the wall thin, composed of angular brown cells, the pore rounded, 5 µm diam. Conidiophores short, undifferentiated. Conidiogenous cells 15-18 µm long, bearing several spores on their somewhat attenuated tips. Conidia 4-5 x ca 1 µm, bacillar, not curved, hyaline, aseptate.
Teleomorph: ascomata immersed apothecia (hysterothecia), opening with a longitudinal split almost the length of the fruit-body; 650-900 x 400-550 µm, shining black, in partially bleached areas, without black zone lines on petioles, and laminae of leaves, narrowly to broadly elliptical with rather acute ends, intraepidermal. Upper wall heavily carbonized, the split lined with hyaline periphysis-like cells. Lower wall a brown, translucent plate one cell thick of epidermoid cells. Interascal tissue of filamentous paraphyses ca 1 µm diam., straight or variously bent and contorted at the tips, not swollen above, forming a thin but compact yellow-tinted epithecium. Asci 92-105 x 7-8 µm, cylindrical to narrowly cylindric-clavate, the apex obtuse or slightly attenuated, tapering toward the base to a short stipe, 8-spored. Ascospores fasciculate, not helically coiled, 38-45 x 1-1.5 µm, filiform, hyaline, aseptate, straight, with a gelatinous sheath 1-1.5 µm thick.
Not formally assessed, but reasonably common and unlikely to be threatened.
On fallen overwintered leaves of Crataegus species.
Widely distribued, from southern England northwards to Skye.