Conidiomata as locules formed in stromata, often multilocular, convoluted and radiating from the centre, probably preceding perithecial formation. Conidiophores hyaline, septate, branched irregularly at the base and above, formed from the inner cells of the locule walls. Conidiogenous cells formed as long terminal branches of conidiophores, straight, hyaline, smooth, proliferating percurrently, collarette and periclinal thickening inconspicuous. Conidia cylindrical to allantoid, hyaline, thin-walled, aseptate, without guttules, often formed in distinct variously coloured masses as globose droplets or tendrils.
Stromata appearing as scattered, small, circular, raised, ± conical to pulvinate pustules, with a variably developed white, brownish or grey ectostromatic disc dotted with black perithecial necks. Entostroma white to greyish and composed of interwoven hyphae with some host cells intermixed in the lower part, well-developed, delimited by a black stromatic zone line, particularly prominent beneath the perithecia, containing few to numerous perithecia. Ascomata perithecia, ± globose with long necks, black, upright to oblique, necks converging, emergent through disc but only just exceeding the upper surface, clustered in compact groups. Peridium composed of dark thick-walled angular cells. Interascal tissue absent in most species, the ostiolar canal periphysate. Asci cylindrical-clavate, with a tapering base, apically thickened, with a refractive apical ring, 4- to 8-spored, I-, becoming detached within the perithecial cavity. Ascospores allantoid to cylindrical, hyaline, aseptate, smooth, without a gelatinous sheath or appendages.
Similar to Valsa but with usually well-developed pale ectostromatic discs and stromata that are bounded by a conspicuous black zone line. Valsella species only seem to differ from Leucostoma by their ascomata with multispored asci.
Causing canker and dieback of twigs and small branches of coniferous and broadleaved trees, continuing to live saprobically following death of the plant tissues. They are likely to be endophytic within living tissues, but more research is needed on this aspect of their biology. Some workers have described them as opportunistic pathogens, infecting plant tissues that are injured or environmentally stressed.