FLORA OF ICELAND elements: Cystopteris fragilis, Brittle Bladder-fern, Tófugras

Cystopteris fragilis; The Brittle Bladder-fern is a relative small fern. The bipinnate fronds are about 10 to 25cm. long. The fronds grow from horizontal rootstocks. The main rachis is black to green and rather slender. It can also break quickly (hence the English name: "brittle"). The primary leaflets are well spaced from each other (leaving a gap between them). The secondary leaflets have obtusely pointed lobes with rather characteristically zig-zag shaped lateral nerves.
The round sori, when young, have rather inflated indusia. They are placed on top of the end-nerves of each leaflet lobe.
The Brittle Bladder-fern is by far the most common fern on Iceland. It grows on stony grounds, very often in lava fissures. It is a species that can grow in dark places where hardly any other plant species can grow.
One special place where this species grows is the Steinahellir cave in southern Iceland. The whole entrance to the cave is covered with the fern. But also inside, where little light enters the cave, the walls of the cave are also covered with the fern. It shows the ability of the species to grow in dark conditions. For the observers it is interesting for one can see here many so-called prothallia, the gametophyte phase of ferns. Gametophytes/prothallia in ferns are very small (usually about 0.5cm - but it differs from species to species) and therefore usually overlooked. Nevertheless, it is a fundamental phase in the life cycle of ferns, which can easily be studied in this cave. Note too, that anyone picking a fern here is cursed - according to legends.
Cystopteris fragilis, the Brittle Bladder-fern is member of the Cystopteridaceae, the Fragile Fern Family. The Icelandic name for this species is Tófugras.