This association is dominated by the small fern Gymnocarpium robertianum, which forms a branched rhizome spreading extensively within the scree. It occurs on mobile or intermittently stable screes formed of limestone, hard claystone or base-rich volcanic rocks. This vegetation type is more common on screes of natural origin than on anthropogenic screes. Its Czech localities are concentrated in the Bohemian Karst and Moravian Karst, but it is rarely found also in other areas with screes of base-rich rocks.