Ferns; the underwater forest

Needle leaf Java fern

The Planted Tank
Ferns, the underwater forest
By Robert Paul Hudson
　
When I think of ferns, the picture that comes to mind is when I would walk underneath a forest canopy of trees that filters out the sunlight creating cool and misty air that makes the entire day feel like dawn. The forest floor is covered in layers of fallen trees and lush ferns and moss. Entering this world stirs something within me as if I am remembering some primordial experience. What better way to bring a sense of raw nature to the aquarium than incorporating aquatic ferns.

Microsorum pteropus
“Java fern” is one of the most heavily used ferns in our hobby because it is so undemanding and considered one of the easiest aquarium plants to grow. In recent years, various regional growth forms and cultivars have been introduced to the hobby. This includes a narrow leaf version, an ultra narrow leaf version, wide leaf version, bullate leaf, trident leaf, and cultivars Windelov, (lace fern) and Tropica.

The native range of the specie is all over tropical Asia. The leaves grow from a thick rhizome that is best not to bury in the substrate, but instead tied to wood or rock. Above water, the rhizome may be planted in loose soil and grown successfully. Leaves of all the variant growth forms carry spores that look like black dots. The spores are more prevalent when the plant has been grown above water. New plantlets will develop from the spores while still attached to the parent leaf. Even a broken leaf will sprout new plants if it carries spores.

Lighting and water parameters are not that critical for java fern. The plants have been known to grow in soft, hard and even brackish water under very subdued light all the way to very intensive light. Growth rate is relatively slow, but the plant will remain healthy and robust from regular fertilization to the water column. The leaves are tough enough not to be bothered by plant nibbling fish and snails.

Ceratopteris, the Indian fern
Ceratopteris, commonly known as Watersprite, is the fastest growing aquatic fern in the aquarium. With moderate light or better and at least 10ppm of C02, this plant will grow as fast as any stem plant. There are four recognized species of Ceratopteris. Cornuta and thalictroides look somewhat alike, except that thalictroides has finer leaves and has long stems, while cornuta is more stout and wider leaf. Thalictroides grows rooted in the substrate while cornuta may grow floating or in the substrate. Pteridoides is strictly a floating plant with large leaves of very variable shape. I wrote about this plant in my earlier floating plants column. The fourth specie is richardii, which has yet to be introduced to the hobby. Once in a great while you may see reference to a variety called siliquosa. This is generally thought to be synonymous to thalictriodes, but some people insist it has distinctively finer leaves than thalictriodes. These species began in India and much of Asia, but has become naturalized around the world. These ferns bring a very light green/yellow color and fine leaf texture to the aquascape with a fast growth rate that helps to to balance a new aquarium.

Bolbitis heudelotii
African water fern to me looks the most like the ferns I see when hiking in the mountain forests. Highly pinnate, and dark green, it has a very earthy look to it. It is a little more demanding than other ferns. It seems to grow very well in acidic water, although C02 addition may compensate, (if the water is too alkaline, the leaves blacken), and it does particularly well in moving water or when placed in the path of a good current such as the out flow of a filter. It’s native African habitat is in very fast moving rivers among rocks and stones. Like Java fern, it is best not to bury the rhizome. There is another Bolbitis specie from Asia called B. heteroclita that is occasionally imported for the aquarium. I have never found this plant to do well and I do not believe it is really best suited for aquatics.

Marsilea
Marsilea is often called water clover, and to look at it you would not think it was part of the fern family. There are 65 species, several of which that grow in shallow water along the edges of ponds, and a few species that adapt well to growing completely under water. The four lobe leaf turns into only one or two lobes underwater, but creates a nice looking carpet just the same. Quadrifolia is the most readily available specie in the USA, and one of the easiest to grow. Other species such as Hirsuta and Minuta are attractive for their smaller size, but spread much more slowly.

Ferns to avoid
Any terrestrial fern should not be put in an aquarium and one such fern commonly seen sold as an aquarium plant is Trichomanes javanicum, otherwise known as Borneo fern or Aqua fern. While it loves humid, damp air and wet soil, it will only slowly disintegrate underwater. There is nothing I hate more than a decaying plant in my aquarium.