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This lichen could only be confused with P. aipolia (see described elsewhere) whose habitat it often shares. However, it differs in two important respects. The most reliable field character is the absence of white speckling on the lobes which is most apparent when the thallus is damp. A dab of Potassium hydroxide (K) applied to the medulla (the layer below the cortex or outer surface) should produce a negative effect, that is, it is K-. [The medulla is revealed by scraping away some of the cortex from a wetted specimen but care is needed as the cortex of P. stellaris is also K + yellow as in P. aipolia]. Throughout Ireland.
Original text submitted by Vince J. Giavarini