Picture taken on the 9th April 2007 at "Gorges du Segre", Bains de Llo, Llo, Oriental Pyrenees, France, on siliceous rock rich in iron, East exposure, 75 º inclination, 1.380 m. alt.,associated to Acarospora sinoptica and Acarospora smaragdula.
Cosmopolite species, upland places up to the alpine stage. In Catalonia it is only mentioned at Montseny mountain . It is a species loving iron rich rocks, wattered and even in windy places.
Saxicolous, siliceous, crustose thallus, normally carmine red but sometimes, as in the current case, brown, cracked-areolate, limited by a black prothallus, although not always visible.Immersed apothecia, black disc, max. 0,5 mms in diameter, round form or elongate if pressed by other areoles. presence of conidia. Easy to confuse with Rhizocarpon oederi, a lot of times both grow together but the latter has gyrose apothecia.
No chemical spot reactions.
I had difficulties in determining this lichen because I was used to the typical coloured form. I always remind the wonderful Nicholson illustration in one of my first books of lichens by Frank Brightman but it was misleading in this case.
A similar colour form can be found at pag. 434 of Frank S. Dobson Lichens book.