Cucurbitaria rhamni  

Anamorph: Camarosporium rhamni Allesch., Microdiplodia rhamni Fuckel fide Mirza (1968), Sivanesan (1984); Pyrenochaeta-like (this research). Conidiomata [Pyrenochaeta]: 50-80 µm diam, ± globose, black, superficial in clusters on the basal stromatic tissue, the walls composed of thick-walled dark brown textura angularis with cells to ca 8 µm diam, with an inner wall layer of hyaline textura angularis. Conidiophores 7-15 x ca 3 µm, formed from the inner wall layer, frequently absent or reduced, proliferating percurrently, terminally and laterally immediately below the septa, periclinal thickening and collarettes inconspicuous. Conidia 2-3.5 x ca 1 µm, bacillar, hyaline, thin-walled, aseptate.

Teleomorph: Stroma poorly developed, visible in (rather old) GB material as a thin black layer below the bark. Ascomata 300-500 µm diam, turbinate, short-stalked and often distinctly flattened, the apex strongly flattened with a conspicuous sunken ostiole, matt black, the surface minutely to coarsely verrucose, in irregular clusters of up to 10. Peridium composed of an outer layer to ca 50 µm thick of strongly melanized thick-walled textura globulosa with cells to ca 10 µm diam and often completely occluded, merging into an inner layer of pale to mid brown slightly smaller, globose to angular cells, the locule lined by thick-walled hyaline glassy flattened cells. Interascal tissue composed of thick-walled branched and anastomosing pseudoparaphyses to ca 2.5 µm diam, eventually fragmenting at the septa. Asci 116-148 x 10.5-12 µm, ± cylindrical, usually rather short-stalked, thick-walled and fissitunicate, the apex rounded with a clear invagination in the inner wall, mostly 8-spored with a few 2- or 4-spored asci within the same ascoma. Ascospores 18-21.5(-23) x 7-8.5  µm, ovoid-ellipsoidal, reddish brown, mucous sheath absent, strongly constricted at the primary septum, the lower cell narrower and more conical than the upper, with 3-5 secondary transverse septa and a single longitudinal septum which does not extend the full length of the spore, the septation rather irregular in arrangement.

The species is recognizable chiefly by its rather small, ovoid ascospores. No material of the Camarosporium and Microdiplodia anamorphs has been seen. The GB material may be distinct from European collections on Frangula alnus, but certainly appears to be a good species of Cucurbitaria.