I think this could be Celothelium ischnobelum but I can find few images to compare with online so I’m hoping someone might be able to confirm, correct or offer comments!
Found on a Hawthorn twig collected in SW Ireland were two small, darkened areas, each with two or three tiny perithecia +/- covered with bark cells.
In section (K) a number of empty, rather distorted asci and an abundance of what appeared to be very long, narrow, multi-septate spores.
The asci were KI (Melzers) negative – but the thallus reacted K+ yellow which it shouldn’t have, though there were a lot of patches of trentepohlia on the twig and other lichens.
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