Hi forum,
I am posting this Dothideomycete on the behalf of Paul Leroy who recently found it on wild plum stones (Prunus cerasifera) in the vicinity of Tours (France).
Ascomata are subglobose 0.5–0.6 mm diam, half immersed with a stout neck. The neck is broadly rounded or slightly laterally flattened, typically with a slit-like or more rarely Y-shaped ostiole. The wall is black, pseudoparenchymatous, thick and leathery, much thinner and less pigmented in the immersed part.
Asci are bitunicate and fissitunicate, short-stipitate, cylindrical to fusiform, with uniseriate overlaping ascospores tending to become biseriate in the mid-part. Apex with a distinct refractive annulus, well seen by contrast in Congo red. Hamathecium of narrow trabeculate pseudoparaphyses. Ascospores 35–38 x 8–9 µm, fusiform slightly inequilateral, 5-euseptate, olivaceous brown at fresh state, end cells smaller and paler, wall verrucose, without sheath.
We considered Trematosphaeria and Lophiostoma in which it might have been placed according to old concepts of these genera but without success. Because of the well-developed ostiolar necks and cylindrical asci with a refractive apical annulus we also considered Navicella but in this genus ascospores are distoseptate and the hamathecium is different.
The unusual substrate and the distinctive morphology of this fungus may remind you something we missed.
Thanks for your suggestions.
Cheers,
Jacques & Paul