Growing on a rough-barked tree (which I failed to note, so provided an image). Unsure if the silver-grey thallus belongs to the species in question or is a host. Spores (3-septate) become brown quite late into maturity. Spore-drop, in water: 19.9-25.5 x 7.6-9.8 µm. Me = 22.4 x 8.7. The spores are quite wide for this genus, even allowing for shrinkage when measured in KOH.
As you can tell, I failed to key it out so any help appreciated.
