Thyriothecium: blackish, up to 280 µm diam., with a clearly visible papil, scattered or less often close together.
Ostiole: 12-20 µm diam, blackish, margin somewhat iregular, without setae.
Shield: composed of radiately, irregular arranged, elongated, brown cells, thickwalled, 1,5-4,5 µm wide, at the margin forming a kind of fringe up to 20 (-30) µm long.
Ascospores: pale grey to yellowish brownish, smooth, more often 1 x septated but also sometimes 3 x septated, with some drops, cilia not seen, 14-20 x 5,5-6 µm.
Asci: bitunicate, 58-70x9,5-12 µm on a short base.
Pseudoparaphyses: cylindric, iregular thick, septated, sometimes branching.

I wonder if this is Arnaudiella caronae. However the spores of this found are somewhat longer and are sometimes 3 septated. Perhaps there is another species?

Arnaudiella caronae (Pass.) Petr., Annales Mycologici 25: 339 (1927) [MB#259925]
https://www.asturnatura.com/fotografia/setas-hongos/arnaudiella-genistae-fuckel-e-mull-1/15764.html
http://ascofrance.fr/recolte/2953/dothideomycetes-microthyriaceae-arnaudiella-caronae

Literature:
Ellis, J.P. (1977) British Microthyrium species and similar fungi. Transactions of the British Mycological Society 67: 381-394
Müller E, von Arx JA. Die Gattungen der didymosporen Pyrenomyceten. Beiträge zur Kryptogamenflora der Schweiz. 1962; 513.
Wu, H.X., Schoch, C.L., Boonmee, S., Bahkali, A.H., Chomnunti, P. & K.D. Hyde (2011) A reappraisal of Microthyriaceae. Fungal Diversity 51: 189-248.