Unknown foliose lichen on birch

Unknown foliose lichen on birch

Observation - Unknown foliose lichen on birch - UK and Ireland. Description: Found on mature birch near a stream. Fruiting bodies on thallus margins - are these isidia? Papery texture, and interesting dark brown underside to the thallus, which seems to curl over in places.

Found on mature birch near a stream. Fruiting bodies on thallus margins - are these isidia? Papery texture, and interesting dark brown underside to the thallus, which seems to curl over in places.