Found on fallen mature beech twig - looks like the yellow fungus/lichen could be associated with the foliose lichen?
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
Cannot remove my earlier suggestion but now agree with synangium's identification and notes.
I must not add it as an ID above, as it will trump the Parmelia ID.
It is also a lichen. I was thinking it might be Candelariella xanthostigma, but looking at photo 2 at high magnification, I see tiny green areoles (islands of thallus), producing bright yellow soredia at their edges.
It is Caloplaca flavocitrina - better known as a species on walls, but it readily grows on damp bark, often in very small patches as is the case here.
Lat/Lng: 50.5966, -3.7251
OS grid ref: SX779788
MIxed deciduous woodland on the edge of Dartmoor