This class comprises pioneer grassland vegetation on sand and shallow soils of rock outcrops, which are frequently disturbed by erosion and various animal and human activities. Plants growing in such habitats face drought stress and considerable temperature oscillations, which select particularly for functional groups of short-lived vernal therophytes, geophytes with a short growing period, succulent plants, and dessication-tolerant mosses and lichens. Such plants usually grow in gaps within loose stands of hemicryptophytes. The class is distributed across temperate Europe.