Parmelia sulcata?

Parmelia sulcata?

Observation - Parmelia sulcata?. Description: Found on fallen oak twig. Looks like it might have been colonised by an alga? The margins are dark brown to black in places, like the edges of burnt paper - is this normal?

Found on fallen oak twig. Looks like it might have been colonised by an alga? The margins are dark brown to black in places, like the edges of burnt paper - is this normal?