Porpidinia tumidula (Sm.) Timdal

      Thallus of 4-8 cm formed of strongly convex squamules rounded at the ends which gives them a globular appearance, upper surface finely cracked and chapped, grayish-white a little greenish in wet weather, pale brownish in dry weather, strongly pruinose which gives it a chalk-like whitish appearance, whitish to pale brownish undersurface. Apothecia forming between the scales, 1-1.5 mm in diameter, disc flat then convex, blackish, not pruinose, concolorous margin quickly excluded. Utriform asci without ocular chamber, with 8 spores. Elliptical, colorless, simple or 1-septate spores, 10-20 x 3-5 µm according to the literature, 10-16 (20) x (3) 4-5 µm according to our measurements. Photobiont: chlorococcoid. Thallus: C-, K + yellow or K-, KC-, P-. Thermophilic species found in cracks in hard limestone rocks.