Anamorph: not known.
Teleomorph: stromata to 500 µm deep. with a lens-shaped to low conical, black, ectostromatic disc to 600 µm diam, surrounding and united with the perithecial necks, extending outward beneath the host periderm as a distinct clypeus, composed of dark brown thick-walled angular cells. Ascomata 500-900 µm diam, perithecial, depressed globose to near-hemispherical, base often strongly concave when dry, upright, neck 400-640 x 100-150 µm, central, black, smooth, immersed, separate, scattered, appearing on the host surface as conical pustules with the torn periderm exposing the rounded apex, barely emergent. Peridium to 45 µm thick, composed of a layer of angular, sometimes slightly compressed, dark brown, thick-walled cells at the exterior and an interior layer of elongate, thin-walled, strongly compressed cells, the neck composed of broad, dark brown, thick-walled, parallel to interwoven hyphae. Interascal tissue absent, neck with hyaline periphyses. Asci 63-90 x 15-19 µm, elongate-ellipsoidal to clavate, somewhat sac-like when mature, with a single discernable wall layer, with a J- refractive apical ring, 16- to 32-spored, becoming detached within the perithecial cavity. Ascospores 16-27 x 3-4 µm, cylindrical to narrowly ellipsoidal, straight to very slightly curved, tapering slightly to broadly rounded ends, hyaline, smooth, becoming 1-septate, very rarely 2-septate.
Closely associated with the GB & I species Phragmoporthe conformis which often occurs on the same twig and has a similar clypeate perithecium but which has 8-spored asci and wider 3-septate ascospores.
On dead twigs of Alnus and possibly also Populus.
From England (Dorset, South Hants, Herefs, West Kent, Middlesex, East & West Norfolk, North Somerset, East Suffolk, Surrey, Warks, Worcs, North East & Mid West Yorks), Scotland (Mid & North Ebudes, Shetland) and Wales (Montgomeryshire).