First lichen (Lecanora campestris)

Since it was installed in the window box nearly two years ago the small sandstone rock in the top right corner has been developing a good skin of vegetation.

There are several mosses, as the picture shows, and the greenish white lichen with purple 'jam tarts' (Lecanora campestris) in the centre of the frame continues to expand. There is also a black encrustation on the rock - I will find out what that is one day. Maybe someone knows?