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The Java Fern
(Microsorium pteropus)

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Reproduction in Java Fern

Java Ferns' reproductive flexibility is one of its great strengths. Aside from airborne spores (which are supposedly rare even in nature) I have found four (4) ways new plants or leaves develop in the home aquarium. One is through the ever creeping rhizome, which sprouts new leaves as it grows in width and length. A second is through the development of tiny plantlet "babies" at the tips of other leaves. This is especially common with leaves that are long or older. Eventually the plantlet grows to about 1 inch and breaks off the mother leaf. This is similar to how Watersprite (Ceratopteris sp.) reproduces, which is in the same family of ferns. "Impatient" aquarists can break off the plantlets early without any harm to either plant. Two other methods of Java Fern reproduction are less frequently described. In fact, I have yet to read descriptions. I have observed that older leaves of Java Fern, as well as large leaves that are transplanted, often develop black "spore" spots on the underside. You can anticipate this when a leaf looks weathered, with more pronounced vein lines. java fernThese spots eventually develop into plantlets, and it has been my experience that these plantlets usually grow quite large and hardy. In fact, they must be broken off manually. It is as if a dying Java Fern leaf wants to "go out with a bang!" One leaf on a plant I had was torn and decayed but still produced babies for a year until I pruned it. The last method of Java Fern reproduction I have witnessed involves planlets growing from the roots. This only happens when the roots are hanging in the water without attachment. I cannot find any documentation of this reproductive method, but nonetheless I have witnessed it. It makes for a very attractive cascading effect, almost like a hanging houseplant. Recently I have discovered little Javas growing inside a cave from the driftwood in my tank. I am not sure if these are from adjacent roots which made their way into the cave, or by spores!

Keeping Java Fern in Your Aquarium

With all its beauty and ease of propagation, I often wonder why Java Fern is not more frequently available in pet shops. It appears well-suited to the low-light and hard/alkaline conditions often found in dealer tanks. The slow growth of Java Fern could be a factor (fish farmers may be impatient too). When you do find Java Fern, it may be planted in the gravel. Having a good idea what Java Fern looks like before you ask for it helps a lot as many dealers are unfamiliar with the plant. When you request some, I recommend you ask for it submerged in water. Dry air is the Achilles heal of Java Fern. This hardy plant needs to keep wet. True it is most often found in the wild as an emersed plant, but as Yoshino & Kobayahi (1993) recently pointed out, it is most abundant in areas exposed to water sprays. The leaves of Java Fern dry quickly, so as you set up its new home, keep it submerged or use a spray bottle to keep the leaves moist as you prepare the tank.

To facilitate acclimation of any new plant, I like to initally add a bit of electrolyte-based water conditioner, such as Jungle's Plant Saver. After purchase, you now have the option of tying it down, planting the roots, or letting it float. The former method is preferred by me. I like to use black thread (which matches the roots) to gently tie down the rhizome to a piece of driftwood. Java Fern seems to grow best when attached to a nice piece of wood and given room to "spread." But there's no harm in tying it to small scrap wood, ornaments, rocks, and gravel. It will grow well there too. Holding the plant down in the gravel by its roots can be cumbersome at first, but eventually it will be anchored by its attachment to bits of gravel. Some people have had trouble acclimating Java Fern initially. It has been suggested that this is often due to the fact that imported Java Fern is collected along brackish coastal areas. However, it will rebound. You may want to ask your dealer where his stock is from and how long has it been in freshwater. Since Java Fern is often found near moving water in emersed form, it likes swift oxygenated water during the evening (hence, the leathery leaves). This is usually no problem in the home aquarium, where powerheads and filters increase oxygen saturation. This is a refreshing change from dealing with flowering plants in search of lots of CO2, which is often not available in large enough quantities in home aquariums.

Java Fern accepts a broad range of water temperatures from the mid-60s to the mid-80s. but is best at temperatures in the mid-70's. Yoshino & Kobayahi (1993) report on a peculiar disease affecting aquatic ferns during periods of high water temperatures. They advise that tank temperatures do not exceed 82 degrees and that any dying leaves or runners be pruned. However, I have never experienced this disease with my Java Ferns in the 4+ years I have grown them. And this includes the usual Jersey summer when my Java Fern tank stays in the mid-80's for weeks at a time. Perhaps I have been lucky. Water hardness and pH ranges are equally liberal. Java Fern is found on jungle floors where soft, acidic water sprays on its leaves, on the edge of mountain streams where near neutral conditions exist, and in the hard, alkaline tanks of African Cichlids keepers who use it as their plant of choice. Aggregate recommendations for Java Fern range from a 5.0 to 8.0 pH with a 2-25 DH. Here in New Jersey, my tap water ranges from 6.6 to 7.8, with a German hardness of 10 DH and my Java Fern grows fantastic. Most experts recommend optimum conditions at a pH of 6.0 to 7.0 with hardness from 2-12 DH.

Lighting for Java Fern is similarly easy. Java Fern does well in subdued to bright light, and unlike other aquarium plants, even seems to prefer more dim conditions. One fluorescent strip light sized over your tank is plenty. In my Java Fern tank, one side is exposed to diffused morning sun from an adjacent room. The ferns really respond well on this side of the tank. I use a trace fertilizer occasionally for the minute amount of potassium required by the fern, or when I see the leaves yellowed, which is a rare occurrence. If you have an unaeratd gravel bed, you may want to occasionally use a ion-excahnge resin such as Aquarium Pharmaceutical's Phos-Zorb to take care of phosphate build-up. But these are routine practices for general planted tanks. Java Fern is most forgiving in these areas. Java Fern is an efficient utilizer of ammonium products ( the preferred nutrient of plants). So unlike the usual recommendation for planted tanks, stocking levels for fish can be higher without detriment to the plant. Ammonium is in smaller quantities in alkaline tanks (where ammonia is more produced as the first step in the nitrogen cycle) but my Javas still do quite well in my alkaline tanks. A good geographic aquarium display using Java Fern could include fish that also prefer cooler, oxygen rich waters. China's Golden Barbs such as Barbus semifascioltus or schuberti, Spanner Barbs from Java (B. lateristriga), or Black-Spot (B. filamentosus), Purple-Headed (B. nigrofasciatus), or Cuming's Barbs from the Sri Lanka mountains would all be geographically appropriate. An aquarium manual some years ago briefly mentioned that a scat ate the leaves of a Java Fern and died. Since then there have been numerous reiterations of this tale with the conclusion that Java Fern is poisonous. The only fish I have seen eat a Java Fern was a team of hungry Goldfish - and they all lived. Clearly this theory needs scientific substantiation. Aside from the pruning strategies already mentioned, your Java Fern will now pretty much take care of itself. It is an extremely economical plant. I have filled up many tanks from just one small plant I received a few years ago. And that's without extra lighting or gravel or CO2 canisters. With Java Fern any hobbyist can have a beautiful planted tank. Even impatient ones.

Originally published in "AquaWorld Magazine".
Published here by permission of anonymous author.

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