On a stone bridge wall, probably granite though not sure; whitish (in some of the other patches)a dirty brownish-white crustose 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.
It is affectionally known as Crab's-eyes.
A genuine common name I belive, not an arbitrarily made up one.
What a strange name! I shall have to look for a crab now to see if they look anything like it!
I have to say that on our university marine fieldcourse recently, when we saw a lot of Crab's-eyes lichen and also a variety of crab species, that the resemblance was less than remarkable.
Lat/Lng: 57.6797, -2.8736
OS grid ref: NJ479658