Porpidia platycarpoides (Bagl.) Hertel

    Thallus crustose, markedly granulose to areolate, areoles more or less convex, minutely papillate or verrucose, whitish to pale ash-grey, prothallus often inconspicuous, blackish to greyish. Apothecia scattered, usually scarce, sessile to slightly immersed in the thallus, 0.5-3 mm diam., disc flat to convex, sometimes umbonate, black, occasionally with a white pruine turning its colour to greyish, exciple thick, swollen, smooth. Ascospores simple, egg or tear-shaped, 15-25 x 7-11 µm according to literature, 15-23 x 8-10 µm according to our measures. Medulla: C-, K+ yellow to red, Pd+ yellow; exciple cross-section: K+ yellow to red. Photobiont: Clorococcoid. Maritime trends, on acids rocks. N.B. Very difficult to distinguish in the field from Porpidia macrocarpa specimen with greyish thallus, and most often apothecia cross-sections are required to proceed to the K reaction. Porpidia cinereoatra has much smaller apothecia, more or less immersed in the thallus and scattered over the areoles, markedly delimited by a black prothallus.