FLORA OF ICELAND elements: Gymnocarpium dryopteris, Oak Fern, Þrílaufungur

Gymnocarpium dryopteris; The Oak Fern is a rather small fern (15 - 30cm). The leaves stem from long horizontal rootstocks. It has a quite characteristic appearance: the first pair of (opposite) leaflets are each almost just as large and rather similar in shape as the rest of the leaf. This makes it appear as if it has three equal blades. Bear in mind though that this first pair is the first 1^e-order in a pinnate leaf-shape. The second pair of 1^e-order leaflets are those which seem to be the first pair of the middle blade. Obviously the first pair is deeper pinnately split than the second pair. One could therefore say the plants have tripinnate leaves. Also, right at the junction of the main rachis to the side rachii of the first leaflet-pair, there is a bended twist in the main rachis, as a result all three "blades" have their leaflets facing upwards. Quite characteristic too, are the very slender dark (black) leaf-stalks, rachii.
The sori lack an indusium. They are round-shaped placed on the end of lateral veins near the margins on both sides of the lobes.
The species is quite common, especially in some western and northern locations. It grows in forests and among bushes, but also in other protected habitats like lava-fissures, hollows etc.
A note on the name Gymnocarpium can be translated into "naked fruit" referring to the absence of an indusium. "Dryopteris" is a contraction of "drys" (ancient Greek for oak) and pteris (fern).
It belongs to the Cystopteraceae, the Fragile-fern family. The Icelandic name for this species is Þrílaufungur.