This is a calcicolous and slightly nitrophilous vegetation type of shaded sites, dominated by Cystopteris fragilis. This species, however, is not confined to calcareous substrata; it can also grow in other associations of Asplenietea trichomanis on acidic rock outcrops. Along with other small ferns, species of nutrient-rich forests are common. The more species-rich stands of this community are found on natural rock outcrops, where some rare relict species can be found. More common, yet species-poorer, are stands on walls and in other human-made habitats such as quarries.