Discussion with Jason Hollinger led me to Oliver Gilbert’s (very good, in my opinion) book “Lichens”, which has a color plate (not so good, in my opinion) captioned, ""The rare arctic-maritime species Lecanora straminea growing on a bird cliff, Flannan Isles." This moved me to acquire some fresh C to confirm the specimen as C+orange, which it is (see newly posted photo).
Brodo (2001) – “There are many other [than L. muralis] lobed species of Lecanora, especially in the west. Some of them contain xanthones in the cortex and either react C+ orange or are fluorescent in long-wave ultraviolet light. One example is L. stamina, which often accompanies L. murals on bird rocks along the west coast.”