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| Do you have questions, want to discuss the issues raised in this column, or read the comments of other aquarists and the answers from columnist Karen Randall? You can do so by going to Aquatic Interactive. |
Equisetum
The genus Equisetum, the “horsetails,” contains two aquatic species, both native to northern temperate areas of the world. Horsetails have erect jointed stems, reminiscent of bamboo. The leaves are whorled and scale-like. The sporangia are held in a rounded cone at the top of the stem. Because they are too large for the average home aquarium, these plants are not of much interest to aquarists, but they are interesting plants for the ornamental pond. I have also seen them used to good advantage in large public aquarium displays where they are allowed to grow emersed, with just their feet in the water.
Isoetes
There are approximately 100 species of quillwort distributed world wide, mostly in the temperate areas. There are species that are submerged, emergent and seasonally submerged. Quillwort is similar in looks to Acorus, with a fan of straight green leaves arising from a central rosette. Unlike Acorus, however, the leaves are rounded instead of flat.
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KAREN RANDALL |
| This attractive tank, owned by Dave Gomberg, is planted predominantly with aquatic ferns, including Microsorum pteropus, Bolbitis heudelottii and the Ceratopteris species sometimes identified as C. siliquosa. |
I think the reason these attractive little plants are not used more in the aquarium is the difficulty of propagation. Propagation by division is rarely successful. They must be propagated sexually, and this is a long, tedious process. Some species will reproduce spontaneously if kept in a small unfiltered aquarium without fish, but even under these conditions, it can be more than a year before young plants develop.
Lycopodium
Lycopodium is a member of the club mosses. The reason I mention it here is that it is not an aquatic plant and is often offered to aquarists in the form of “princess pine.” Do not purchase these plants! They die slowly, but they will die when submerged in the aquarium. In some states, Lycopodium sp. are threatened in the wild and protected by law.
Marsillea
There are 65 species of Marsillea distributed in the tropical and subtropical areas world wide. Most require an emergent period to produce sporocarps, but the plants can also be easily propagated vegetatively under emersed or submersed conditions. There are so many species it can be difficult to identify a particular specimen with certainty. There are probably more species that would adapt to aquarium life than are currently in commercial propagation.
Most have four leaflets when grown emersed or floating, leading to the common name of “water clover.” Most show only one leaflet in the submersed form. Marsillea is the only fern with leaves capable of assuming a “sleep” position. For ornamental pond use, some of the species I’ve seen offered include M. drummondii, M. schelpiana and M. mutica.
For aquarium use, the most hardy of those currently available seems to be M. drummondii. This Australian species is quick to produce a lawn-like effect similar to Glossostigma if given good light and adequate concentrations of CO2. It is more tolerant of high general hardness than Glossostigma, which makes it a useful plant for those of us with harder water.
Two other species that are less tolerant, but are occasionally offered for sale, are M. exarata and M. crenata. M. exarata is sensitive when transplanted and needs soft water and strong light to do well. M. crenata is really not suitable for permanent submerged existence. Under good conditions, (soft water, strong light and supplemental CO2) it may work as a short term “lawn plant.” Eventually, however, it will either die out or begin to reach toward the surface with floating leaves.
Microsorum
The genus Microsorum includes some 60 species, some of which are known to be aquatic. The genus is found in Southeast Asia. Microsorum (mistakenly spelled as “Microsorium” in many older texts) has simple leaves, sometimes three, and rarely five lobes. Spores mature on emergent fronds and presumably are distributed by the wind.
In the wild, Microsorum grow in moist tropical areas, usually along the edge of streams. They are frequently found in the spray zone of waterfalls. Microsorum is more salt tolerant than many plants, and is often collected from brackish water areas. It presents a problem for aquarists when these wild collected plants are offered for sale. The leaves that have grown under brackish conditions often deteriorate under softer aquarium water conditions. The plant may recover if the rhizome is left in place, but the novice aquarist often gives up at this point and throws the “lifeless” rhizome away. It is usually better to purchase captive-propagated specimens. These plants are already acclimated to aquarium conditions and will not deteriorate the way wild ones can.
Currently, there is only one species, M. pteropus, that is widely cultivated on a commercial basis under the common name, Java fern. It is possible that at least one other species may find its way into the aquarist’s hands from time to time. There are at least five variants of Java fern available either commercially or from other hobbyists in the U.S.
’Tropica’ produces leaf plantlets, like the other forms of Java Fern, but the plantlets do not reliably show the leaf extensions seen on the parent plant. The only way to assure the leaf extensions will be seen in a propagated specimen is to propagate by division of the rhizome.
’Windeløv’ produces large numbers of leaf plantlets, and these grow true to the form of the parent plant. They do, however, detract somewhat from the fluffy symmetrical shape of the parent plant. To maintain the attractive mounded shape of the parent, the leaf plantlets should be removed as they develop. As with other Microsorum the plant is also easily propagated by rhizome division.
All forms of Microsorum pteropus are not only beautiful, but hardy, low-maintenance aquarium plants. They tolerate a wide range of aquarium conditions, including very low light levels and hard, alkaline water. Their tough leaves resist damage by all but the most determined herbivores. Still, they appreciate and will grow faster under good conditions.
Like Bolbitis, Java ferns do best attached to a piece of driftwood or stone. The rhizome should not be buried, but they will tolerate having the roots placed into the gravel if the gravel is large enough in size that the substrate stays fairly aerobic.
It should be remembered that Microsorum feed directly from the water column under most conditions. In tanks with a lot of competition from fast-growing plants, they can benefit greatly from regular additions of nutrients to the water column.
Java fern is a tremendously useful plant in a primarily “fish” tank. Because it tolerates low light and takes nutrition directly from the water, it can be grown successfully in tanks with high nutrient levels that would encourage algae growth with stronger light levels. At the same time, it removes waste products from the water, providing a healthier, more stable, environment for the fish. Java fern is often one of the first plants with which budding aquarists are successful.
Pilularia
There are six species of this small creeping fern, all of which are aquatic or amphibious. Pilularia is similar to Marsillea, but with simple (undivided) leaves, even when grown emersed. Young leaves emerge in the tight spiral “fiddle head” shape typical of ferns. Pilularia are found in the temperate tropical and subtropical regions of the world. They are not common even in nature, however, and distribution can be very spotty.
This is a plant you often see mentioned in older books, but I have never run across it on a sales list. The plant was used more frequently in the early years of the hobby, probably in part because coolwater tanks were more common. Still, I think the major reason it is rarely seen in aquaria is that it is not in commercial production. P. globulifera is said to be the best species for aquarium use, but P. americana is probably well worth some experimentation as a foreground, “lawn” producing plant in coolwater tanks.
Salvinia
There are approximately 10 species of Salvinia. The plant, however, has been spread world wide in tropical and subtropical areas, and a number of hybrids have resulted as well.
Salvinia is a floating fern with an unusual form. It appears to be composed of segments with two small opposite leaves with roots hanging below. These “roots” are not roots at all, but a third, finely divided leaf segment! The plant has a distinct stem, which is irregularly forked. At each node, there are two floating leaves with the finely pinnate leaf below. The floating leaves are photosynthetic, while the pinnate leaf below is not. Instead, this leaf works as roots might in another plant, to gather nutrients for the use of the plant.
Salvinia can reproduce via spores, but under aquarium conditions or in the ornamental pond, propagation is mainly vegetative and can be explosive. The plant can reproduce quickly enough to be a nuisance, blocking light to plants below. On the other hand, it is an excellent nutrient sponge and can be extremely useful in controlling algae, both because it provides some shade, and also because it removes nutrients from the water so quickly. The hanging submersed leaves make excellent fry cover in a spawning tank, and the excess are eagerly eaten by herbivorous fish, making for a constantly renewable green food source.
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