• Macro and habitat suggest Hymenoscyphus s.l., confirmed by micro.
• The spores and excipulum suggest H. s.s.
• Seems to be H. caudatus.

Habitat: On dead stem of Juncus effusus, on the ground, damp when found, damp and muddy area, mixed deciduous woodland of mostly Castanea sativa, part of a large area of agricultural land being 'rewilded' (Knepp Estate), Low Weald, southern England, early November.

Apothecia: ~5 on a short piece of stem, < ~ 1 x 1 mm, whitish-yellowish, short stipitate.
Low magnification: Cupulate then more discoid, possibly growing from below the epidermis and associated with splits in the stem, pruinose appearance, receptacle and disc more cream to yellowish, receptacle internally whitish, disc opaquer, apparently remaining slightly concave, resp. margin remaining slightly raised, possibly eventually flattening, indistinct and uneven, stipe narrow cylindrical, more whitish or translucent.

Asci: Simple septa, rings bb, Hymenoscyphus-type, when immature (with fusion nucleus) and flaccid then elongated-lageniform with apex acute-rounded, with no thickening and could be mistaken for paraphyses but the apices and contents are clearly different, 8-spored but rarely only 4-spored with noticeably larger spores.

Spores: Ellipsoid to lacrymoid, shape quite variable, when heteropolar with the apex rounded to hemispherical and the base more acute, often asymmetric to +/- scutuloid in profile view, sometimes with a central restriction, OCI ~4, multi-guttulate in the asci, then often 1-3 large to medium and many small LBs towards each pole, apparently uninucleate but some free spores with a single? (transverse) septum, these spores slightly wider, some also with darker walls, large spores usually noticeable wider, more limoniform.

Free regular-size spores in water:
(15.9) 16.6-18.8 (20.1) × (4.3) 4.7-5.3 (5.5) µm, Q = (3.2) 3.23-4.0 (4.4), N = 27, mean = 17.8 × 5.0 µm, Q mean = 3.6.

Free large spores in water: 25.3 x 8.4 um, 20.8 x 6.3 um.

Paraphyses: Cylindrical, apex slightly to medium clavate-spatulate, with Hymenoscyphus type VBs at the apex, lowly-refractive, yellowish, some reddening with trauma, contents with moderate dextrinoid reaction.

Medullary: Text. porrecta-intricata.

Ectal: Text. prismatica.

Marginal cells: Starting at the upper flanks, broadly cylindrical or sometimes clavate, apex rounded to obtuse, occasionally more irregular, with yellowish contents at the apices, with strong dextrinoid reaction.