Lichen below high water

Lichen below high water

Observation - Lichen below high water - UK and Ireland. Description: Crustose lichen growing on siliceous sandstone cliff below high water mark. Smooth white areolate thallus. Black prothallus boundary between adjacent patches. Black lecideine apothecia with white pruinose surface covering. Possibly Buellia subdisciform

Crustose lichen growing on siliceous sandstone cliff below high water mark. Smooth white areolate thallus. Black prothallus boundary between adjacent patches.
Black lecideine apothecia with white pruinose surface covering. Possibly Buellia subdisciformis.