Trapelia involuta (Taylor) Hertel

      Thallus with a subsquamulosus aspect made up of isolated radially growing areoles, 0.5-1.5 cm in diameter, these areoles quickly take on a lobed appearance with a slightly crenellated margin that is sometimes quite distinct (flower appearance! ), these lobes are more or less flat and not very thick, surface a little satiny in the shade, pale gray, pale brownish gray; with age and growth these isolated areoles can aggregate and form a relatively thick crust, strongly cracked around the areoles which nevertheless remain quite distinct (in principle!), hypothallus inapparent. Late-appearing apothecia, rare to few in number, initially forming a small excrescence on the thallus then sessile, disc flat, pinkish brown, brownish then blackish-brown, more or less concolorous margin. Ascospores elliptical, simple, 19-24 x 9-12 µm. C+ red, K-, KC-, P-. Pioneer species of stones and siliceous rocks, particularly in scree or quarry debris.

Species very close to Trapelia glebulosa and synonymized by certain authors, but the latter differs by minimal variations of its DNA and in the field by its single thallus not formed by the aggregation of isolated areoles, more convex and with apothecia of appearance earlier.

N.B. Watch out for Placopsis lambii also C+ red but which has flat and radially incised soralia and marginal lobes and also to Trapelia placodioides which has a continuous, cracked thallus and is usually infertile.