Diploschistes scruposus (Schreb.) Norman

   Thallus crustose, rather thick (1-3 mm), the surface uneven to verrucose, pale greyish in well-lit areas, greyish tinged with yellow or green when shaded, prothallus white. Apothecia numerous, urceolate, closed and immersed in the thallus at first, then emerging and opened when mature, 1-3 mm diam., disc black, pale grey pruinose, margin conspicuous, uneven, sometimes more or less crenulate or fluted, looking like an old tire. Asci 4-8 spored. Ascospores ellipsoid, muriform, 20-40 x 10-18 µm. Photobiont: Trebouxia. C+ red, K+ yellow, KC+ red, Pd-.  Not especially maritme, but not rare on the sea shores on acid rocks and walls. N.B. The 'maritime' taxa seem diferent from those inlands, but up to now they hare hardly distinguishable and we use the species name sensu lato, until the genus revision; worth to mention, there is on the schist highly exposed  hilly crests a taxon  with pale beige-brown thallus, Pd+ yellow (see pictures below).*