Siliceous rock faces and cliffs, mostly of hard crystalline rocks, soft mica schist and some volcanics, in the boreal and arctic biogeographical regions, though not including sea cliffs with salt spray influence or very wet, dripping vertical rock faces. The vegetation consists of a limited vascular flora growing in crevices and on ledges, with epilithic bryophytes, lichens as well as micro-algae on rock faces, overhangs and in all kinds of sheltered microsites. Although the rock types are all base-poor, they show marked variation in their chemical composition and stratigraphy and can harbor a great diversity of vascular plants and cryptogams in many different assemblages, disposed in many microhabitats.

[Data on this habitat are missing in the European Vegetation Archive.]