On exposed and nitrophilous natural rocks and artificial substrates (concrete, asbestos, old walls and gravestones), rarely on the dust-enriched base of old isolated trees.

Belgium: Mar.: AR, Fl.: C, Brab.: AR, elsewhere: AR-C.

Luxembourg: Ard.: AR, Lorr.: AC.

France: Mar.: RRR, Boul.: RR, Pic.: RR, Mosan, Ard., Lorr.: AC-C.

Lit.: Boul.: 72, Ca: 160-161, Ho: 209, La66: 474, Qu: 119-120, WS: 48, 95.