This vegetation type occurs on shaded outcrops of acidic siliceous rock such as sandstone, granite, gneiss or shale. It is usually dominated by Polypodium vulgare and contains species typical of the forest herb layer which are adapted to shaded conditions and low-pH soils. The moss layer is well developed, often in the form of continuous carpets of pleurocarpous mosses such as Hypnum cupressiforme. This vegetation type is rarely found in human-made habitats, except shaded dry-stone walls built without mortar. It is common in Bohemian sandstone areas and in deep river valleys of the Bohemian Massif.