Umbilicaria deusta (L.) Baumg.

     Foliose thallus forming a rosette formed by a single lobe fixed by its center at the beginning then by several with age, 3-8 cm in diameter, margin more or less undulating and sometimes lacerated, typically turned downwards in dry weather. Upper surface smooth or a little pleated, dark brown, blackish-brown in dry weather, greenish-brown in humid weather, partially or entirely covered with cylindrical isidia, simple or branched, flattened,...; lower surface without rhizines, smooth to areolate, brown, more blackish towards the center. Apothecia very rare, 1-1.5 mm in diameter, gyrous disc, black. Ascospores, hyaline, elliptic, 8-15 x 4-8 µm. Photobiont: chlorococcoid. Medulla: C+ red, K-, KC+ red, P-. Common mountain or alpine species growing towards the base of siliceous rocks above the tree line.