Trapelia glebulosa (Sm.) J. R. Laudon

    Thallus crustose-squamulose, made of squamulose areoles more or less separate, usually dispersed but sometimes mostly contiguous or overlapping, crust forming, squamulose at the edge, squames 0.2-0.4 mm diam., convex to markedly convex when separate, bright to white-bluish, whitish, white-glaucous. Apothecia 0.4-0.8 mm diam., almost embedded within sqamules at first (eye-like), then sessile, disc flat  to convex or markedly convex (and even globose when moist), sometimes uneven, brown-red, dark red to very dark red, exciple very thin to absent when mature, minutely squamulose, paler or whitish. Ascii 8-spored, clavate to cylindrical, K/I-, 90-130 x 20-25 µm (according to our own measures). Ascospores colourless, simple, ellipsoid, external wall tender, easily torn within a K solution (potentially suggesting polarilocular ascospores), 15-26 x 7-13 µm.  Photobionte: chlorococcoid. C+ red, K-, KC+ red, Pd-. On siliceous rocks (granite or schists) or more frequently on stony grounds where apothecia are more developed.

Cf. Trapelia coarctata of which the thallus is granular without squames.

Cf. Trapelia obtegens which is sorediate.

N.B. Some authors separate Trapelia involuta which has larger and isolated areoles or grouped but appearing well separated, a less blue-green coloration in humid weather and rare darker brown or blackish apothecia of late appearance.