Attractive pattern found on several rocks along path up from Roman Road to Fan y Big summit.
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.
The pattern of concentric circles is typical of this species.
Thistle - many thanks for your feedback - John
The concentric rings of apothecia are a good character, and indeed this lichen used to be called Rhizocarpon concentricum.
However, other crustose lichens can have concentric rings of apothecia too. Porpidia crustulata can look quite similar at times, and the common Rhizocarpon reductum has a variant (var. cinereum, but name not validly published) with a cracked, silver-grey thallus and distinctly concentric rings of apothecia. I have a page on this ready to go up on my site (if/when I have time to continue with my site), but I am still trying to get a good photograph of typical R. reductum, common though it is.
Lat/Lng: 51.87, -3.409
OS grid ref: SO030199