Trapelia elacista (Ach.) Orange
Thallus crustose, rather thin (especially towards the margin), continuous, strongly cracked, pale greyish in dry weather, greyish-greenish in wet weather, with gray-pink or yellowish-brown areas. Apothecia numerous, scattered over the entire thallus, at first in the form of small rounded, whitish excrescences, closed at first then opening by one or more sinuous and irregular slits, revealing the light brown disc then dark brown and even almost blackish at the end, margin formed by whitish shreds sometimes doubled by a circular furrow (appearance of a bowl on a saucer!). N.B. A new apothecia can sometimes arise in an old one! Spores simple with large guttula, elliptical, 14-24 x 8-12 µm. C+Fleeting red, KC+ red, K-, P-. Quite rare (or confused?) pioneer species on siliceous rocks, sometimes on the ground on stones, or broken bricks in wetlands.
Cf. Trapelia coarctata very similar but whose development and appearance of the apothecia are different.