Carex agastachys is the Eastern parallel species of the Western Carex pendula s.str., the crossover between the two species runs through Germany. Carex agastachys has red margins of the ligules and obovate nutlets in the fruits (widest near one end), while Carex pendula s.str. has white margins of the ligules and elliptical nutlets (widest in the middle). Both species are not only native wild plants, but also cultivated as ornamental plants, and are running wild, too.
The two species have only been differentiated since 2018. This page shows my older photos, on which the species are not distinguishable.