Peltigera membranacea (Ach.) Nyl.

   Thallus foliose, spreading in large patches, to 20-30 cm across, lobes entire and without folioles, 1-3 cm wide, tips down-turned or up-turned according to orientation, upper surface markedly bullate or embossed without foliole, grey-bluish when dry, grey, pale grey-brownish, brown-olive when moist, pale grey minutely farinose notably towards the margin, lower surface white or cream, with raised white veins not flattened, rhizines simple, white, dispersed, dagger-like. Apothecia more less abundant, ellipsoid or saddle-shaped, organized horizontally (usually as large as tall or larger in some cases), brown-red to brownish. Ascospores fili-fusiform, 3-5-septate, 50-73 x 3.5-4 µm. Chemical spot tests negative. Common, on covering mosses on rocks and tree trunks. Close to Peltigera canina that  grows on ground notably on calcareous dunes and with a lower surface displaying rhizine tufts feather-like. Also close to Peltigera hymenina of which apothecia  are nail-shaped (i.e. taller than larger), upper surface not bullate, lower surface with simple rhizines feather-duster-like. If clusters of schizidia are visible, see Peltigera praetextata. N.B. One typical fan-shaped form may be found on submerged rocks located in streams or on banks of small rivers characterized by the development of Osmunda regalis, Peltigera membranacea forme saxicole.