This association includes vegetation on sun-exposed and dry outcrops of acidic rocks. A typical species is Asplenium septentrionale, in some places accompanied by the rare fern Woodsia ilvensis. Other species mainly include widespread generalists of acidic soils, although some rare relict species can also be found in some places. This vegetation type is rarely encountered in some areas of the Bohemian Massif, most often in deep river valleys.