Picture taken on the 16 March 2008 at Garraf mountains, near Plana Novella, Olivella, Barcelona, on hard liemstone, vertical position, North oriented, 300 m. altitude.
Crustose lichen, thallus white or white grey immersed, almost not visible, with yellow tinge due to escarification of the cortex appearing the yellow Trentepohlia algae. Lirellae in heaps, dense, up to 2 mms long, black colour.
No spot reactions.
Determination following Wirth, but with certains doubts due to the complexity of the genus.
See Wirth et alter (2004) Guiía de Campo de los Líquenes, musgos y hepáticas, Edit. Omega, pag. 264.