Picture taken near Querigut, Ariège, Oriental Pyrenees, France, on beech-tree, 1.100 m. altitude, very humid forest, growing with Lobaria pulmonaria.
It is the first time I see it in the Oriental Pyrenees, very rare. It is a more common species near the Atlantic coast and always in old forest with very clean air.
Foliose lichen, thallus yellowish green in this case because it was dry, blue-grey when wet. It is a large lichen, lobes ridged. Under-surface tomentose with white areas. Coarse, grey-blue soralia. No apothecia.
Medulla K+ yellow, P+ orange
Cyanobacterium as photobiont.
See: F. Dobson, Lichens, pag. 255 and C. Perez et alter, Guía dos liches de Galicia, pag 246.