On siliceous to slightly calcareous rocks, also on walls, bricks, mortar, etc.

Belgium: Mar.: R, Fl.: R, Camp.: R, Brab.: R, Mosan: AR, Ard.: AR.

Luxembourg: Ard.: R, Lorr.: RR.

France: Mar.: RR, Boul.: RR, Ard.: RRR, Lorr.: RRR.

Lit.: Boul.: 67, NL84: 13, NL87: 20, NL92: 152, NL93: 43, VGH: 114, Hoffmann & Van Rompu (1995), Zwaenepoel et al. (1994: 37).