Syn.: R. ambiguum (Schaer.) Zahlbr.

On siliceous rocks, either on natural outcrops or on artificial substrates (incl. bricks), sometimes over Aspicilia caesiocinerea.

Belgium: Mosan: RRR, Ard.: AR.

Luxembourg: Ard.: R.

France: Ard.: RRR.

Lit.: DG: 25, Mü1: 144, NL92: 162, Giralt & van den Boom (1996: 81).