Lecanora quercicola

This species superficially does not look all that different from a small Lecanora chlarotera except that it occurs on the old bark of ancient trees whilst L. chlarotera is typically a species of young smooth bark. The often pruinose, red-brown coloured  lecanorine apothecia on a grey thallus are all Pd- and K- (unlike L. chlarotera that has a K+ yellow thallus). The conidia need to be observed to separate it from other small Lecanora species.L. quercicola has sickle-shaped conidiospores over 1.5 microns wide and between 8 and 12 microns long. (RGW)

Photo: Ray Woods