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(Map updated: 11 August 2009)

This pale grey to white, rock-inhabiting crustose species occurs commonly on acid rocks in upland areas where it can be found on drystone wall field boundaries as well as on outcrops and boulders. The small, white soralia are reminiscent of those of P. amara or P. lactea but it is K+ brown-red, and C-. The soralia are not bitter tasting. It is scattered throughout upland Ireland.

Key characteristics

• It is best separated using chemical spot tests. The C-, K+ brownish red and Pd+ red reactions serve to confirm it. The similar Pertusaria lactea is C+ red
• Never encountered with discs.

Original text submitted by Simon Davey