White crustose lichen with white fruting parts ('jam tart' fruits). Found on sycamore tree in urban area.
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 could be, but Lecanora albella also has white-pruinose discs.
You need to spot test the apothecia with a tiny drop of C - L. carpinea is C+ yellow, L. albella is C-.
Spot test details:
As Jenny says, this cannot be ID'd without chemical testing.
Lat/Lng: 53.33248, -6.25058
OS grid ref: SG171901
Busy urban road, along Grand Canal, Dublin