Anamorph: conidiomatal locules formed within the stromata, often multilocular, convoluted and radiating from the centre, probably preceeding perithecial formation. Conidiophores 6-25 µm long, hyaline, septate, branched irregularly at the base and above, formed from the inner cells of the locule walls. Conidiogenous cells not clearly distinct morphologically from the conidiophores, usually formed as long distinct branches, straight, hyaline, smooth, proliferating percurrently, collarette and periclinal thickening inconspicuous. Conidia 4.5-8 x 0.5-2 µm, cylindrical to allantoid, hyaline, thin-walled, aseptate, without guttules, often extruded in sticky orange-red tendrils.
Teleomorph: stromata 1-2 mm diam., truncate-conical, prominent, containing 6-12 ascomata. Ectostromatic disc 300-350 µm diam., almost pure white, with the black tips of the perithecial necks just emerging. Entostroma greyish to brownish, composed of interwoven hyphae with some host cells intermixed in the lower part, well-developed, delimited by a conspicuous black stromatic zone line, particularly prominent beneath the perithecia. Ascomata perithecia, 200-625 µm diam., ± globose with elongate necks 200-550 µm long and 100-300 µm diam. at the base, black, upright to oblique, necks converging, emergent through the disc but only just exceeding the upper surface. Peridium 10-12 µm thick, composed of dark, thick-walled angular cells. Interascal tissue absent, but neck periphysate. Asci often predominantly 4-spored and then measuring 35-40 x 8-9 µm, alternatively 8-spored and measuring 41-48 x 8-9 µm, cylindrical-clavate with a tapering base, apically thickened, with a refractive I- apical ring, becoming detached within the perithecial cavity. Ascospores 12.5-17 x 2.5-3 µm in 4-spored asci, 10-15 x 2.5-3 µm in 8-spored asci, allantoid to cylindrical, hyaline, aseptate, smooth- and thin-walled, without a gelatinous sheath or appendages.
Not formally evaluated, but the species appears to be reasonably common and widely distributed and would probably be assessed as of Least Concern.
Distinguished by its almost pure white ectostromatic discs, along with its host preference.
Valsa sordida occurs on the same host plants, but has less prominent ectostromatic discs that are grey or tan rather than white, slightly smaller ascospores and lacks a black zone line delimiting the entostroma.
Associated with a number of different Populus species, including P. alba, P. balsamifera, P. x canadensis, P. nigra and P. tremula. There is a single report on an undetermined Salix species.
Widely distributed throughout GB&I, from Cornwall to E Inverness and reported from both the Irish Republic and Northern Ireland.
Considered to cause canker and dieback of twigs and young branches, at least in some circumstances associated with wounding or environmental stress.