Order: Lecanorales Family: Rhizocarpaceae
Species: Rhizocarpon lavatum
Photos: On stones in wall. Gougane Barra, Cork, SW Ireland.
Identified by John Douglass
Grey to pale ochre-brown thallus, greener when wet or shaded, smooth or cracked. Prothallus weak or absent. Apothecia +/- flat, discs black, not pruinose, thick persistent dark-brown margins.
Asci 8-spored, spores muriform, colourless, 30-40 x 14-18 Ám.
Occurs on damp siliceous rocks near upland streams and lake edges. Chemical reactions negative.
Similar: Rhizocarpon reductum. Usually K+ yellow, P+ orange.
Rhizocarpon lavatum. August 2009