Stromata appearing as scattered, ± circular, low or truncate-conical pustules erumpent through host bark, exposing a well-developed black-brown to greyish ectostromatic disc 0.2-2.0 mm diam through which the perithecial necks emerge, darkened area somewhat extended beneath the host bark; entostroma well-developed, brownish, composed of hyphae and rounded-angular cells intermixed with host cells and angular crystals, sometimes poorly developed beneath the ascomata, containing a cluster of perithecia in the lower part, lacking any distinct zone lines within the substrate.
Ascomata 200-500 µm diam, perithecial, globose or mutually deformed, with long necks, black, upright to oblique; necks 250-700 µm long, convergent or remaining separate, with just the upper part emergent, formed in clusters in the lower part of the entostroma. Peridium composed of brown, thick-walled, rounded-angular cells at the exterior, merging into an interior layer of compressed, hyaline cells, neck composed of elongate, brown, thick-walled cells. Interascal tissue composed of paraphyses, broad, ribbon-like at first but soon disappearing, the neck periphysate. Asci 50-73 x 7-12.5 µm, clavate to cylindric-clavate, the apex somewhat truncate, thick-walled particularly in the upper half, with a single discernable wall layer, 8-spored, with a refractive J- apical ring, becoming detached within the perithecial cavity. Ascospores 11-16(-18) x 2-3(-5.5) µm, narrowly ellipsoidal to near fusiform, often tapering slightly more at one end than the other, straight to slightly curved, hyaline, 1-septate, the septum usually median but sometimes dividing the spore nearly 2:1, slightly constricted at the septum, smooth, often with a small cylindrical hyaline appendage at each end.
Anamorph: Fusicoccum-like. Conidiomata formed in locules 0.5-1 mm diam within the stroma, often towards the periphery, with a poorly defined wall. Conidiophores filiform, hyaline, septate, smooth, irregularly branched, formed in the basal part of the locules. Conidiogenous cells cylindrical, hyaline, smooth, with a minute channel and collarette, proliferating percurrently. Conidia of two types; alpha-conidia 6.5-12.5 x 4-6 µm, ellipsoidal to ovoid, acute at one end and obtuse at the other, hyaline, simple; beta-conidia 9-19 x 1.5-3 µm, cylindrical to fusiform, straight or curved, hyaline, simple, smooth.
Description contributed by Graham Kinsey
Rarely reported from GBI, but quite probably overlooked.
Amphiporthe hranicensis has ascospores that lack appendages, and conidial locules formed in a ring around a central stromatic structure; it is associated with Tilia spp. rather than Castanea.
In bark of dead branches of Castanea sativa
Known from England (West Sussex, Worcs and North East Yorkshire).