Description: Thallus inapparent, not lichenized, consisting of colourless hyphae. Perithecia black, matt, 0.13-0.25 mm across, circular, at first immersed in the substratum, then hemispherical to flattened and c. 0.05-0.07 mm high, the ostiole located centrally. Involucrellum dark brown to greenish black, c. 10-15 μm thick, extending beyond the perithecium in a basal fringe, composed of pieces of bark intermixed with greenish-black hyphae; exciple thin, poorly evident, pale throughout; pseudoparaphyses 2-2.5 μm thick; hymenial gel I-. Asci 8-16-spored, clavate-ovoid, 40-66 x 18-25 μm, bi- and fissitunicate, with a broad, truncate apical beak. Ascospores 1-septate, hyaline, narrowly fusiform, arcuate, 13-25.5 x 3-4.5 μm. Photobiont absent. Spot tests: K-, C- KC-, P-. Chemistry: without lichen substances.
Note: on the smooth bark of Populus, especially P. tremula, more rarely of Salix. Earlier records from southern Italy, being dubious, are not accepted here (see Nimis 1993: 418).