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 a lot of this is just a layer of a green alga (Chlorophyta), but there may be a lichen mixed in (not Lecanora expallens but maybe a Lepraria). A microscope is often necessary to be sure in the absence of any lichen fruitbodies. However, as I have said in other observations by this poster, I click the picture to get an enlarged view, but when I click the resulting link for the original photograph it is much too small, and in this case lacks definition.
Algal mats are common on tree trunks and on stonework.
Sorry if "this poster" sounds impersonal, but all we have is this Open University "code"!
Lat/Lng: 52.5344, 1.1654
OS grid ref: TM147976
This was on a Sycamore tree in the Church yard at Ashwellthorpe which I found whilst doing the Opal Air survey