The Ladder Spleenwort (Asplenium adulterinum) belongs to rare and threatened species in the Czech Republic, and it is strictly bounded to serpentine substrates. Several localities of this fern are in northern Moravia, where its populations are regularly monitored. This contribution summarizes the results of monitoring of A. adulterinum in the Chrastický Hadec Natural Monument since 2006, and ... [Show full abstract] provides a list of current flora of this protected area. While the population with approximately 2,900 clumps seemed to be stable up to 2016, it underwent a 40% decrease within the next five years. Drought period, increased competition pressure or natural population dynamics are considered as possible reasons. The change in abundance of the Ladder Spleenwort is not accompanied with changes in the flora composition of the area. A total of 214 vascular plant taxa were recently found here, out of which four belong to the endangered species, but A. adulterinum remains the only strict serpentinophyte of this locality.