Porpidia macrocarpa (DC.) Hertel & Knoph.

    Thallus thin, smooth to rimose, seldom thick, areolate to more or less verrucose, pale grey, grey-greenish, often partly covered with rusty spots, prothallus inconspicuous or wavy and blackish. Apothecia usually numerous, scattered over the thallus, sessile, to 3 mm diam., disc flat then convex and finally markedly convex, sometimes gyrose or with 'multiple' exciples, black, seldom powdered with grey pruine, exciple more or less wavy apparently dividing apothecia as if there were several exciples, thick (0.15-0.2 mm wide), persitent for a long time, black. Utriform asci of 70-90 x 15-30 µm according to our measurements. Colorless, simple, elliptical spores, 16-20 x 5-12 µm according to the literature, 15-21 x 7-12 µm according to our measurements. Photobiont: chlorococcoid. Medulla: K +/- yellowish, P +/- yellow-orange, I-. Species not especially maritime but common on acid rocks. This species is difficult to separate in the field from Porpidia platycarpoides with coastal affinities, K + yellow to red, P + yellow and from Porpidia crustulata with smaller apothecia with a thinner margin. N.B. It is probable that there are many taxa under this name because this species is very variable.