Species: Racodium rupestre
Photos: Below overhang, acidic rock. Gougane Barra, Cork, SW Ireland. Identification needs confirming
The thallus forms small patches of dark brown or black, +/- felted filaments. Very similar to Cystocoleus ebeneus but the mycobiont hyphae are straight and not entwined or contorted.
Can be locally common in upland areas on shaded, humid, +/- vertical siliceous rocks. Also found below overhangs where it is sheltered from direct rain. Chemical reactions negative.
Identification is very uncertain, photographs are probably of the cyanabacteria Stigonema
Racodium rupestre. September 2009