The class Asplenietea trichomanis includes vegetation of rock outcrops, walls and stabilized screes composed of large stones and boulders. In such habitats, vascular plants are confined to crevices and small ledges. Bryophytes and lichens are common, the former colonizing both ledges with soil accumulation and bare rock surfaces, the latter extending also to rock surfaces. In this habitat plants experience various forms of stress, including nutrient and water shortage and large temperature fluctuations. Compared to the Alps, Carpathians or southern European mountain ranges, Asplenietea trichomanis vegetation in the Czech Republic is species-poor and contains very few relict species. Individual sites usually form small patches surrounded by other vegetation types on well developed soils. The most common and typical species are competitively weak ferns, such as Asplenium spp., often accompanied by species spreading from surrounding forests or grasslands.