AQUATIC HORTICULTURE		BY KAREN RANDALL

KAREN RANDALL

Contrary to most published information, the author has found that Acorus gramineau var. pusillis is a plant that can sometimes do well under permanent submersed conditions if it is carefully acclimated.

The Flowering Plants

I will also include plants that are often offered for sale as “aquarium plants,” but are not really suitable for long-term submersed culture. I am doing this for two reasons. First, so new aquatic gardeners can avoid the disappointments that accompany the purchase of such plants, and second, because many are beautiful in their own right and deserve to be considered for use in terrarium- or paludarium-type setups.

To make it easier for you to figure out how a particular plant fits into the scheme of things, remember that the kingdom is the major unit of classification of living organisms. It divides plants, animals, fungi and so on. The kingdom is further divided into the phylum, class and family, in descending order. These groups can be further divided into subgroups. Finally, we get to the genus and, ultimately, to the species.

It is important to remember, however, that taxonomy is always in a state of flux. Depending on whether the latest research on a group of plants (or animals) is done by a “lumper” or a “splitter”, you will find old names being replaced by new names and plants that were considered a separate species being added back as a variant of another species.

Part of the problem is that the people doing the classifying will always have differences of opinion or will make mistakes. A bigger problem is pinning down exactly what makes one “species” different from another. The more we learn about genetics, and the more actual DNA analysis is done on various groups of organisms, the slushier the boundaries become. Add to that the huge number of naturally occurring hybrids and man-made varieties (cultivars), and it’s no wonder its a jungle out there!

As I write this column, the scientific names I will be using are, to the best of my knowledge, correct. But please bear in mind that even if they are correct today, they could change tomorrow. So, while it’s important to try to hang as accurate a tag as possible on the plants we discuss, don’t get hung up on names. Don’t let the fact that you can’t pin down the exact identity of a particular specimen spoil your enjoyment of a good plant.

On the other hand, when passing a plant on to another aquarist, it is best not to guess at a name. Even if you can’t identify a plant to the species level, most of the time you can be pretty certain of the genus. It is much better to pass a plant on simply as a “Vallisneria sp.”, than to add more incorrect names to the plethora that are currently in use.

Acorus
Family: Araceae
Distribution: Northern Hemisphere

There are several species in this marsh plant genus, but only the smallest, Acorus gramineus var. pusillis from eastern Asia, is at all suitable for use under permanent submersed conditions. Most references state that these plants inevitably die under aquarium conditions, although they may persist for several months before deteriorating.

I did find one book, however, Encyclopedia of Water Plants by Jiri Stodola, that claimed, “Plants cultivated out of water usually die in an aquarium. Only by making the change gradually can it be done with success.” This is the only reference I have been able to find to support my personal experience with the plant.

I have been growing this variety for many years. It increases slowly, but I have kept it in a number of tanks and have been able to share cuttings (divisions) with a number of friends. If you would like to try this attractive little plant, I would suggest that you obtain a division from another aquarist. If this is not possible, try to slowly acclimate your newly purchased plant by raising the water level over a period of time.

If you do obtain a specimen that has become adapted to submersed life, you will find it undemanding as far as water chemistry is concerned. It is said to do slightly better under cooler temperatures, but does fine in my tanks, which are kept at temperatures between 76 to 78 degrees Fahrenheit.

Like most marginally aquatic plants, I suspect that it probably does better with at least moderate light levels. The lowest light I have grown it under has been 2 watts per gallon. As with most other very slow-growing plants, Acorus gramineus var. pusillis is best kept in a tank without problem algae, because it does not grow fast enough to outgrow aggressive algae infestations.

Alternanthera (synonym: Telanthera)
Family: Amaranthaceae
Distribution: Tropical and temperate areas, mostly in Africa and the western hemisphere

There are approximately 170 species of Alternanthera, some of which have been used as terrestrial garden plants for some time. In the wild, most species are marsh plants that can withstand submersion.

At least one species has been found to be suitable for permanent submerged existence under aquarium conditions, although there are probably more species with aquarium potential than are currently being commercially propagated and distributed. Two species, Alternanthera reineckii and Alternanthera sessilis (and several varieties of one), are commonly offered commercially.

Alternanthera reineckii
Common name — scarlet hygro

This is an extremely variable South American species. Most of the Alternanthera commercially available under different “species” names, are actually variants of A. reineckii. Some of the names I’ve seen are A. cardinalis, A. lilacina and A. rosaefolia.

A. reineckii is the only Alternanthera species currently in commercial propagation that is suitable for long-term aquarium growth. It is a striking plant with bright red stems and leaves that vary from bronze to green on the top, and are brilliant scarlet below. Because of its bright color, it makes an excellent contrast plant.

The problem with this plant is that it is not easy to grow. It does best under strong lighting with supplemental CO₂ and regular trace element supplementation. Under conditions to its liking, it grows quite quickly, and will need regular topping. The top sections can be replanted, while the bottoms will branch just below the area that is trimmed, causing a bushier growth. Make sure, however, that a stand is not allowed to become too dense or the lower parts of the plant will suffer from lack of light.

Alternanthera sessilis (non-aquatic)
Distribution: Warm tropical areas worldwide

This species really does not adapt well to permanent submersed conditions. But it makes a beautiful addition to a terrarium or paludarium, where it can get its head above water. The leaves and stem are glossy and such a dark maroon that they are almost black, while the undersides of the leaves are bright red. The numerous tiny flowers are set in white bracts, and grow at the leaf nodes. While quite small, they add an attractive accent note to the dark foliage.

Alternanthera ficoides ’Bettzickiana’ (non-aquatic)
Common name — Hedge (Green, bronze or gold)

There are other species of Alternanthera commercially produced in three or four color varieties. The normal green, a red or bronze color, and a light yellowish one. All of these are regularly offered as aquarium plants, although none will survive long term submersion. As terrarium plants, they could be quite useful.

Aglaonema sp. (non-aquatic)
Family: Araceae
Common Name — Cast iron plant
Distribution: Malaysia

As its common name suggests, this member of the Arum family is a very sturdy plant. It also has very attractive foliage. It is a perfect candidate for emersed growth at the edge of a heavily stocked fish tank, where its root system can act as a nutrient sponge, while the leaves remain above water. It does not, however, tolerate long term submersed conditions.

Ammannia
Family: Lythraceae
Distribution: Tropical and sub-tropical areas worldwide

There are approximately 30 species in the genus Ammannia, most of which inhabit wet areas. It seems likely that there are more species that could be of use in the aquarium than are currently in cultivation. There are two species commonly offered in the trade, although I have also come across plants that didn’t fit either of these species exactly. Whether these other plants are a different species, hybrids, or simply a variant is unknown.

The plants are usually cultivated emersed, as the emersed growth is tougher and better able to withstand the rigors of shipping. This can, however, mislead people, as the emersed growth is very different from that seen in the aquarium. It tends to be fleshier, with shorter, rounder leaves, a thick stem and very little of the pink or bronze coloring that makes these such attractive aquarium plants.

The aquarium care of all species currently available is similar. All require strong light, good substrate and regular additions of trace elements to produce good color and prosper. All benefit from the addition of supplemental CO₂. Do not allow the plants to become shaded by floating plants or crowded by neighbors.

Ammania gracilis
Distribution: Tropical Africa

This attractive stem plant is the less demanding of the two species commonly available. As with all Ammannia species, the leaves are opposite and decussate. The leaves of A. gracilis are slightly wider than those of A. senegalensis, and are quite flat. The color ranges from green with a rosy tinge under marginal lighting conditions to a lovely soft pink or bronze under better lighting. In fact, the common name for this plant in German is the “cognac plant.” I find that this is a species that definitely benefits from some soil at its roots, whether the substrate itself contains soil or the plant is placed in a pot with soil. It can easily be grown emersed, where it will flower and set seed.

Ammannia senegalensis
Distribution: South and East Africa

A little more fussy than the previous species, A. senegalensis is still worth the effort as a good contrast plant. The leaves, which are thinner than those of A. gracilis, twist downward, adding to the visual interest of the plant. The color is often darker than gracilis, but tends more toward brown than pink. Under good conditions, it is still a slower grower in the aquarium than the previous species, and does not stand up to algae infestations well. The stems of submersed specimens can be brittle, so handle carefully when planting. Like A. gracilis, it is quite easy to grow emersed.