Placidium lacinulatum (Ach.) Breuss

    Thallus squamulose, squamules round, tightly appressed to the substratum except towards the margins, slightly turned up, 5-10 mm across, rather thick, 0.3-0.5 mm, upper surface brownish, brown-greenish when dry, greenish when moist, lower surface darker with rhizines, more or less numerous, simple or branched, 0.3 mm wide and to 15 mm long (these rhizines are easily breakable and may be difficult to observe, requiring a specific attention), squamules are lain on a large black fibrose matt. Perithecia pyriform to subglobose, immersed in the thallus, 0.4-0.6 mm diam., invollucrellum absent, excipulum not blackish. Ascii cylindrical, 90-100 x 10-15 µm according to our measures. Ascospores broadly ellipsoid to ovoid, simple, colourless, 12-16 x 5.5-7.5 µm according to literature, 11-15 x 6-7 according to our measures. Pycnidia numerous, laminal, visible as black dots, conidia ellipsoid, 3-4 µm long, Photobiont: Chlorococcoid. Chemical spot tests negative. Uncommon, highly variable with many different varieties already described, on ground, in dry calcareous dunes (Toninion sedifoliae). Very close, and often confused with Placidium squamulosum  that is very similar by its characteristics but devoid or with small rhizines, on calcareous rocks without black fibrose matt underlying. See  Placidiopsis custani  of which the squamules are slightly turned up, margins swollen and ascospores 1-septate. See also Endocarpon pusillum that differs by its branched rhizines and muriform ascospores.*