Nice spotting, Adrián!
They are lichens. To identify them correctly I would need a higher amplification but most probably the white one is Parmelina tiliacea and the yellow one could be Xanthoria parietina. Yau can check it here: http://www.lichens.lastdragon.org or also in the "lichens" mission: http://www.projectnoah.org/missions/8624860
Comments (2)