• Macro and habitat suggested Ciboria, and C. batschiana.
• Confirmed by micro (spores, etc.).
• Some aspects remind me of Monilinia (johnsonii that I found in spring).

Habitat: Locally numerous but only found in one area, only growing from acorns of Quercus robur, some acorns still easily recognisable but pericarp always broken and loose, apparently growing on the cotyledons, slightly enlarged, blackened, somewhat decayed and mummified appearance, shallowly buried in leaf litter, damp area under mature trees, limited undergrowth, mixed deciduous woodland, Low Weald, England, late-September, after lots of rain.

Apothecia: Medium size, diameter < 13 (16) mm, stipe < 20 x 2 mm, length of stipe apparently environmental, initially cupulate, becoming more shallow and eventually discoid, caespitose, in groups of ~2-6 per acorn or cotyledon, receptacle and disk medium to dark reddish-brown (well camouflaged), darker with maturity, smooth and dull appearance, conspicuous wrinkling and some blackening around the base of the receptacle near the stipe, margin narrowing quite suddenly, usually slightly upturned, not exceeding the disc when mature, whitish when immature and blackish at maturity, round but slightly lobate in parts, undulating in maturity, stipe appears stromatised (blackened and burnt), sinuous, narrowing and darkening towards the base, tough and fibrous appearance, disc broadly plano-concave in maturity, blackish in the middle and often with small dark spots when (over) mature, usually umbonate, touching apothecia apparently fusing, sometimes with abundant whitish hyphae around the substrate.

Asci: Cylindrical-clavate, croziers, rings strongly bb, form seems typical of Sclerotinia, apex rounded to subtruncate when turgid (different views?), hemispherical to more acute-truncate when flaccid, uniseriate but slightly overlapping when turgid.

Spores: Irregularly ellipsoid-cylindrical, asymmetric in profile view, sometimes slightly reniform, poles rounded but usually slightly heteropolar with the base more attenuated, some spores more elongated, apparently more common in lower spores, ~2-4 tiny and shadowy LBs and two nuclei visible inside, apparently aseptate, germinating from the poles or the sides, usually one outgrowth.

Free living spores in water (not germinating): 9.2-10.7 (11.9) × 4.4-5.4 (5.6) µm, Q = (1.7) 1.8 - 2.3 (2.5), n = 30, mean = 10.1 × 5.0 µm, Q mean = 2.0.

Paraphyses: Cylindrical, often branching towards the apex, apex slightly to medium inflated and usually irregular to slightly antler-like (propoloid?), hymenium appears peachy colour but no VBs seen.

Excipulum etc. seem typical for Ciboria (at least several species seem to share the general structure).