Confidence: I'm as sure as I can be.
Notes: As iSpot offers the 'agg.' option, I am using it. I think it is true X. candelaria, which in any case is the more likely on open rock surfaces. But some of the lobes are very broad for that species and more like X. ucrainica, which generally occurs on nutrient enriched bark. Lobe width and dorsi-ventral flattening are under environmental control. The two species are apparently valid, but characters used to separate them are unreliable.