On rain runnel on beech trunk.
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.
I think you are correct see http://www.lichens.lastdragon.org/Arthonia_radiata.html
There are some excellent links near the bottom of the Fungi and Lichens 'Groups' page (click 3rd above).
Certificate in Contemporary Science (Open)
Lat/Lng: 52.3568, 0.5698
OS grid ref: TL750763