Corticolous, on all kinds of deciduous trees, in open or in forest conditions, rarely saxicolous, on siliceous rocks or sandstone walls.

Belgium: Mar.: CC, Fl.: C, Camp.: AR, Brab.: AR, Mosan, Ard., Lorr.: CC.

Luxembourg: Ard.: C, Lorr.: CC.

France: Mar.: R, Boul.: AC, Pic.: AR, Mosan, Ard., Lorr.: CC.

Several chemotypes have been recognized in the study area (with protocetraric acid, with hypoprotocetraric ac., and with salazinic ac.), but none of these merits recognition of a separate taxon.

Lit.: Boul.: 73, Ca: 126-127, Ho: 227, La66: 451-452, La68: 79, Qu: 134-135, WS: 56-57, 109, Diederich (1985a: 25).