I found this tiny lichen amongst some moss on a Sycamore in West central Scotland. It looks like a shrunken Hypogymnia but I’m struggling to come to any resolution on ID. I’d appreciate any pointers. K- and C- by putting tiny pieces in reagent on a slide.
Scale on rule is 0.5mm/1mm. The photos are the best I can do with my phone and macro lens.

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Thanks for any help provided.