Placidium squamulosum (Ach.) Breuss.
Catapyrenium squamulosum (Ach.) Breuss.
Thallus squamulose, composed of large squamules more or less round, isolated or clustered, not overlapping, more or less thick and lobate, closely appressed to the substratum except towards the margins, somewhat turned up, 5-7 cm across, upper surface olive-brown when moist, leather, brown-reddish when dry, lower surface darker, without rhizines, lying on a mat of rhizoid hyphae forming a network. Perithecia numerous, immersed in the squamules, visible as conspicuous black dots or minute craters (ostioles) surrounded by a paler zone; they may also be slightly prominent on the lower surface. Ascospores colourless, ellipsoid, simple, 12-15 x 5-7 µm. Pycnidia laminal, numerous, visible on the upper surface of squamules as black dots. Photobiont: Chlorococcoid. Chemical spot tests negative. Rare or understated, on mossy calcareous grounds and sometimes in dry calcareous dunes, seldom in the calcareous rock crevices. N.B. This species is highly variable and very close to Placidium lacinulatum, based on their macroscopic, microscopic analyses and their habitat. The latter differs by the rhizines on the lower surface of squamules.*