Anamorph: conidiomata pycnidial, 500-600 diam and 200-270 µm high, oblate, erumpent through bark tissues, with a distinct papillate neck and ostiole. Conidiomatal wall ca 25 µm thick, composed of small-celled clear brown parenchymatous cells. Conidiogenous cells 8 - 12 x 1 - 2 μm, formed in irregular clusters from a septate conidiophore. Conidia 4.5-5 x 0.8-1.2 μm, hyaline, cylindrical to allantoid.
Teleomorph: ascostromata 900-1700 x 500-700 µm, 200-300 µm high, elliptical to fusiform in face view, strongly domed in horizontal view, erumpent through bark or appearing superficial on wood where the bark is lost, scattered to aggregated and occasionally coalescing, dull to shining black, with a very conspicuous longitudinal cleft extending the whole length of the ascostroma. Peridium with lateral walls 90-130 µm thick, 40-60 µm thick below the hymenium, composed of many layers of cells intermediate between textura angularis and intricata, strongly melanized and completely occluded at the sides and apex, with an inner layer of small-celled ± hyaline flattened cells at the base. Interascal tissue of copious branched and anastomosing trabeculate pseudoparaphyses 1-1.5 (-2) µm diam, immersed in a thick gel layer, and a dark brown melanized epithecium in the cleft region. Asci 170-210 x 31-39 µm, clavate to clavate-cylindrical, short-stalked, the apex rounded, thick-walled and fissitunicate, with a well-developed ocular chamber, with eight (rarely fewer) ascospores. Ascospores arranged biseriately, 31-41 (-55) x 13-18 (-21) µm, clavate to clavate-fusiform, the apices obtuse, complex-muriform, 5- to 12-septate (or more), with 0-3 longitudinal septa in each segment or with oblique septa, golden brown when mature, thick-walled, with a conspicuous gelatinous sheath1-3 µm thick which sometimes becomes pigmented.
In GB&I, not formally assessed but is currently quite common and widespread. Its preference for growth on Fraxinus is likely to pose a threat in the future.
In GB&I, primarily associated with ash (Fraxinus excelsior); also reported from Cornus, Populus, Quercus, Salix and Syringa species. Recorded from a very wide range of woody plants on a global basis.
Scattered throughout GB&I from Aberdeenshire and W Sutherland southwards to S Devon, also reported from various localities in Ireland, N Ireland and Wales.