Dermatocarpon leptophyllodes (Nyl.) Zahlbr.

    Thallus foliose, restricted to a single lobe, 4-7 mm across, attached by a single holdfast but its aspect suggests a large squamulose thallus composed of dense colonies, lobate, lobes intertwined, 3-5 cm across, upper surface without or with little pruine, pale grey-greenish with purple tinge when moist, brown-grey to dull grey when dry, lower surface smooth to slightly veined, dark grey-brownish, brown. Perithecia usually numerous, immersed, 0.15-0.30 mm diam., pycnidia rather similar to perithecia, numerous but smaller, immersed, ostiole blackish. Ascii 8-spored, clavate. Ascospores simple, colourless, narrowly ellipsoid, 15-22 x 5-8 µm according to literature, 13-22 x 4-7 µm according to our measures. Photobiont: green algae. Chemical spot tests negative but hymenium gel is I+ burgundy hemiamyloid, medulla I-. N.B. The iodine reaction is more or less difficult to perform according to sample hydration level. Rare, montane or sub-mountain, on siliceous rocks regularly flooded in unpolluted rivers and streams, often together with Dermatocarpon luridum or slightly above. The latter is composed of a single poly-lobate thallus, with larger lobes, greener when moist, medulla I+ red. See also  Dermatocarpon meiophyllizum of which the lower surface is black, more or less veined.