We've fern again. This time I show you Gymnocarpium drypoteris (L.) Newman (“Oakfarn” in English; “Eichenfarn” in Germany). This species belongs to the Genus of Gymnocarpium, a member of the Woodsiaceae family (in some literature the species still belongs to the Dryopteridaceae).
It's a small fern with lime green, triangular frond and stalk without any glands. However the best feature about this species are the last pair of leaflets, which are as big as the rest of the frond, giving the Oakfern a charismatic look.
The oakfern prefers shady, montane forests with acid soils. I found this one on an excursion to the “Sauerland” at the edge of a road. It was the same place I found the beech fern Phegopteris connectilis (Michx.) Watt