AQUATIC HORTICULTURE		BY KAREN RANDALL

KAREN RANDALL

The Aponogeton

For many people, this is as far as it goes. They use the bulbs as disposable aquarium decorations, just as many terrestrial gardeners plant tulip bulbs each fall, only to pull the plants up after the flowers fade and plant new ones the next fall. But, as with spring flowering terrestrial bulbs, many Aponogeton are perfectly capable of long-term performance if their needs are adequately met.

Aponogeton are native to warm areas of Africa, Asia and Australia. There are now naturalized populations in South America and isolated areas in the warmer parts of Europe as well. The species in the hobby are mostly Asian, with a few species from Madagascar, and the occasional Australian representative.

As with many aquarium plants, exact identification can be tricky. Not only do Aponogeton sp. hybridize quite readily on their own, but commercial aquarium plant growers have also taken advantage of this fact. They have purposely produced a number of man-made varieties (cultivars) in their attempts to bring us plants that are not only beautiful, but also sturdy, long-lived aquarium residents.

As might be guessed from the heavy rhizome developed by most species, Aponogeton sp. are adapted to life in areas where growth is not possible year round. For some species, this means periods of cold, for others it means periods when the conditions become too dry. While some types of plants are able to produce a different type of foliage and survive dry periods in an emersed form, Aponogeton sp. have solved the problem by simply reverting to a resting state during these periods.

Not all Aponogeton require a dormant period. Many, particularly aquarium hybrids, will continue to grow for very long periods of time — in some cases, up to several years.

Because the genus is so widespread, the needs of different species can be quite diverse. This means that there is an Aponogeton species that will work for almost every aquatic gardener. We will look at specific requirements for each plant under its species heading. For now, let’s discuss some general needs of Aponogeton.

While those “wonder bulbs” from the department store will sprout under almost any conditions, Aponogeton are really no different from other aquatic plants in terms of the care they require. If you are satisfied with temporary, replaceable aquarium decorations, it really doesn’t matter how, or whether you care for them beyond dropping them into a container of water. If, however, you would like to enjoy long term success with a beautiful specimen, you must be willing to provide it with good growing conditions. This means adequate lighting, a nutritious substrate and a steady supply of CO₂ and other nutrients.

Most Aponogeton flower readily under cultivated conditions. In general, Asian species will carry one flower spike (inflorence) per stalk, African species will carry two, and Madagascar species may carry more. However, due to the number of hybrid Aponogeton found in the hobby, the number of inflorences will sometimes only give you a clue to the parentage of your particular plant.

Aponogeton flowers are often (although not always) self fertile. It is quite possible to produce viable seeds by gently brushing an inflorence with a soft brush or even your finger tip to distribute the pollen. If the plant is self fertile, the fruits, called “water berries,” will develop along the flower stalk within a matter of days. In time, the flower stalk will begin to decay and the fruits will float free. Within another day or two the fruits will split open and the seed will drop to the bottom of the tank, where it will quickly germinate. If the tank is not heavily stocked, it is possible that a few baby plants will survive.

If you would like to maximize your yield, it is wise to remove the mature flower spike to a small, quiet fish-less aquarium with the fruits still attached. If this tank is set up with good growth conditions (i.e., good substrate, good lighting and adequate nutrients), the sprouts will attain adult size quite quickly.

Many Aponogeton will eventually enter a dormancy period, even under aquarium conditions. Whether the plant will be able to break dormancy and come back to full vigor depends, to a large extent, on the care it received during its last growth cycle. The Aponogeton must store enough energy in its rhizome to carry it through dormancy, and then sprout enough leaves that the plant can resume normal photosynthesis. If it has not received enough light or has not had access to the nutrients it needs, it will not be able to build these reserves.

Some Aponogeton are fine if left in place in the aquarium during dormancy. Others, particularly the cool water species from Madagascar, do better if the rhizome is removed to a container of damp sand and left in a cool dark location for a few weeks. The refrigerator is too cold for most species. A dark corner of the basement is a better choice. After four to six weeks the rhizome may be returned to the aquarium. If the plant was able to store enough energy during its last growth period, it should break dormancy and begin to sprout within a week or so.

Aponogeton boivinianus

Aponogeton boivinianus is a species that is native to the northern parts of Madagascar and neighboring islands. It is not common even in its home territory, and can be difficult to keep going long term under aquarium conditions. It is possible that this is because the conditions under which it occurs most frequently in nature — fast-moving streams and rivers — are hard to duplicate under aquarium conditions.

This is quite a large plant in the wild, with petioles up to 18 inches. The leaves are dark green and bullate, up to a foot long and 2 inches wide. It makes a striking centerpiece plant for a large tank. It requires a fairly nutritious substrate, but will not tolerate a substrate that becomes strongly anaerobic.

Aponogeton capuronii

This is another of the beautiful species from Madagascar. The long slender leaves are deep green, fantastically ruffled, and so stiff to the touch that they may be mistaken for cellophane. Like the previous species, A. capuronii can be touchy under aquarium conditions. It seems to prefer cool, clean, soft water.

Aponogeton crispus

Aponogeton crispus is a very variable southeast Asian species. It is also found to hybridize quite willingly even in the wild, making positive identification difficult. Still, because of the beauty of this species and its relatively low cultural demands under aquarium conditions, it has become a mainstay in the hobby. Most of the generic Aponogeton “wonder bulbs” are this species or a hybrid carrying a good percentage of A. crispus genes.

The leaves, which grow very quickly, range in color from light green to reddish brown, and have wavy edges. It flowers willingly under even marginal conditions, producing a single spike of white flowers that are generally self-fertile. Young plants are easy to raise as long as they can escape the predations of fish, and the tank receives adequate nutrition.

For some reason, the myth has developed that flower spikes of A. crispus (and other Aponogeton) should be snipped before they develop fully, lest they rob the parent plant of strength. It is only under poor growth conditions where this could be a serious problem, and under those conditions, this practice will only delay the death of the plant, not prevent it.

Aponogeton madagascariensis

As its name would suggest, Aponogeton madagascariensis is yet another species from the island nation of Madagascar. This distinctive plant has been well known in the hobby for many years and has frustrated many aquarists. The wide, elongate leaves are missing the tissue in between the veins, giving the appearance of loosely woven green cloth. This has lead to the common name of Madagascar lace plant.

The Madagascar lace plant needs a fairly nutritious substrate, but does not tolerate a substrate that becomes anaerobic. For this reason, many aquatic gardeners have found that it does best with small plants placed around the base that can move water and oxygen through the root zone. Some of the smaller Cryptocoryne work particularly well for this purpose.

Aponogeton madagascariensis has the potential to become a very large plant if the conditions are to its liking (it can easily take over one third of a 70-gallon tank), so it is important that it not be crowded by other larger plants. It must be maintained in a clean, algae-free environment, as the leaves easily become algae infested and are almost impossible to clean. While there are occasional reports of a specimen doing well in a warm water tank, the species comes from cool water in the wild and has a better chance of doing well if temperatures are kept on the low side in the aquarium.

Unfortunately, even experienced aquatic gardeners find this species to be difficult, with the occasional plant prospering, but most fading away to nothing in a matter of months. The plants are incredibly beautiful, and worth a try in spite of the high cost, but don’t be too disappointed if it doesn’t do well for you.

Aponogeton natans

This Asian species is found in Sri Lanka and India. As an aquarium plant it does not have much to recommend it, as the leaves are mostly floating, with only the long slender petiole below the surface of the water. This growth habit blocks light to the other plants in the tank.

What Aponogeton natans has in its favor is that it is extremely hardy. For this reason, growers have used it to create hybrids that have the decorative characteristics of other species, but are less likely to go dormant under aquarium conditions.

Aponogeton rigidifolius

From Sri Lanka, Aponogeton rigidifolius is an oddball among the Aponogeton. It does not produce the tuber-like rhizome of most Aponogeton species, nor does it go dormant. Instead, it grows a long woody rhizome similar to that of a Java fern. This grows just under the surface of the substrate and gets longer and longer with age. The leaves grow up off this rhizome and the plant can easily be propagated by rhizome division.

The plant tolerates harder water than many other species, and its leaves are large, varying in color from rusty red on the edges of the newer leaves to a pleasant dark green on the older ones. In my opinion it is one of the most useful Aponogeton species for the aquatic gardener because it won’t go dormant and leave a hole in your carefully designed aquascape!

Aponogeton ulvaceus

Aponogeton ulvaceous is another of the beautiful and delicate Madagascar species. Its large pale-green leaves are translucent and lightly ruffled. Like the other Madagascar species, it does best in water that is slightly cooler. Fortunately, this is one of the species that has been widely crossed with A. natans, and many of these hybrids have the pretty foliage of the ulvaceous parent, and a little more vigor from the natans side of the family.

Aponogeton undulatus

Found in several southeast Asian countries, Aponogeton undulatus is another family oddball. Unlike the other species in the genus, it is viviparous. It produces entire young plantlets on stalks, similar to the way many Echinodorus species reproduce. These plantlets can be removed from the parent plant and set out on their own in the aquarium when they are large enough. Otherwise, the plant is not too different in looks from many other Aponogeton. It has the typical tuber-like rhizome and long dark-green leaves with a ruffled edge.

This is another plant that has been crossed with A. natans. I have purchased plants as Aponogeton natans that have gone on to produce stalks of plantlets. In this case, the hybridization was probably not such a great idea. The plants were large, vigorous and reproduced freely. Unfortunately, because they produced only floating leaves, they also quickly blocked all light to the plants below. I didn’t keep them in my collection for too long!