Fissidens fontanus

Fissidens fontanus, the spring fork-tooth moss (German: “Quell-Gabelzahn”*), also known as Octodiceras fontanum and O. julianum, is a true aquatic moss and grows submersed in rivers and lakes. It is common in North America, but also occurs in Central America, North Africa and the warmer parts of Europe. In Germany it was initially found only in fountain basins in south-western Germany, but has spread strongly since the 1960s and has meanwhile been recorded in almost all larger rivers. Among other places, it occurs in the lower reaches of the Rhine and the Elbe. This moss apparently copes with very small amounts of light, since in the Rhine, for example, it grows on stones below the low-water line and is located at a depth of more than 2 m at medium water levels and more than 4 m at high water. It can be found, among other places, on embankment walls under bridges, where fewer algae grow because of the shade. At the natural sites F. fontanus is often blackish in colour because of diatom growth.

Although this beautiful aquatic moss is widespread and grows very well in aquariums, it became known in the aquarium hobby late, probably in the 1990s. Of all the Fissidens species introduced so far, F. fontanus is the easiest to keep submersed. This species quickly gained popularity and is now frequently used in aquascaping. F. fontanus is imported from Asia as “Phoenix moss”, where it is only cultivated and is not native.

Fissidens fontanus is a delicate, filigree-looking, dark green moss that attaches itself to wood or rock with rhizoids and forms tuft-like or lawn-like stands. Like all Fissidens species it has two-ranked leaves; the small leaves are arranged in one plane along the stem, so that the shoots are reminiscent of palm fronds or feathers. From most other Fissidens species it differs, however, in its soft, limp texture and its very narrow leaves. The sparsely branched shoots can grow to at least 10 cm in length, but mostly remain much shorter. In air F. fontanus dries out quickly. When dried it is very brittle.

There are five further, very similar Fissidens species in Africa, Australia, North America and southern South America which, together with F. fontanus, belong to the subgenus Octodiceras and are likewise true aquatic mosses. They are not yet known as aquarium mosses, but would probably also be suitable as such. The species of the subgenus Octodiceras are distinguished by microscopic details of the leaves and by the position of the spore capsules on the plant.

The species Fissidens fontanus itself is very variable, and different forms of this species are cultivated which differ from one another under the same conditions, above all in size. They are in the trade, for example, as Fissidens spec. and, mistakenly, as “F. nobilis”. (The true Fissidens nobilis is a completely different-looking, much larger and more robust species.)

(For more, see “Culture” and “Design”)

*)The German names Gabelzahn and Spaltzahnmoos are a translation of the Latin name Fissidens (“split tooth”) and refer to the tiny so-called peristome teeth, which sit in the opening of the spore capsules and are split in Fissidens species.