AQUATIC HORTICULTURE		BY KAREN RANDALL

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Aquatic Plant Overview Continued —
On To The “Cs”

The genus Cabomba has long been a mainstay among commercially available aquarium plants. Unfortunately, it has enjoyed this position not because it is such an excellent aquarium plant, but because one species, C. caroliniana, is native to the southeastern United States and is easy to collect, bundle and sell to pet stores for very little money.

While Cabomba is quite a pretty plant, its downfall in aquarium culture is that it demands light levels far in excess of those found in the average aquarium. The result is that for years, people have been buying this plant, allowing it to disintegrate, and buying some more because it is cheap.

Another problem with Cabomba caroliniana is that it is labeled a “noxious weed” and banned in a number of states because it has invaded many waterways where it was not originally a native. While most of these introductions have been the result of plants hitchhiking on the propellers of fishing boats, it is important that aquarist not contribute to this problem. Do not ever introduce non-native aquarium plants into local waters!

That said, Cabomba can be a very beautiful aquarium plant. All species and varieties require very strong light and a photoperiod of close to 12 hours. Most do best in soft water, although some will tolerate harder water with adequate amounts of light and supplemental CO₂. These plants must be kept in clean, essentially algae-free tanks. Once infested with algae it is virtually impossible to salvage them.

Probably the most common species of Cabomba offered for sale is C. caroliniana, and, for good reason. Not only is it a native and easily collected from the wild, but it is also the hardiest species available. Its bright green foliage is quite attractive and it produces kidney-shaped floating leaves and small pink to white flowers if allowed to reach the surface of the water. It requires strong illumination (a minimum of 3 watts per gallon), but is less light hungry than some other species. It will also tolerate slightly harder water. It is tolerant of water temperatures from the low 70 degrees Fahrenheit right through the mid 80s if its other needs are met. There are several wild occurring varieties of C. caroliniana that can be collected by aquarists with an interest, but they are not seen commercially with any frequency.

In addition to the wild varieties, there is also at least one other cultivated variety of C. caroliniana that makes its way into the hobby with some regularity. This C. caroliniana ’Silbergrune’ was developed by the Hans Barth Aquatic Nursery of Germany. In this pretty variety, the laminae are twisted, so that the lighter underside of each leaf segment can be seen spiraling along with the greener top of the leaf. This gives the plant a lovely silvery appearance, and led to the cultivar name of “silver green.”

Another species sometimes sold is C. aquatica. This is a South American species and is even more finely pinnate than its North American cousin. The effect is a plant that is much more luxuriant, which moves with the slightest water current around it. Unfortunately, this is an even more demanding plant than C. caroliniana, which requires stronger light, softer water and, in most cases, supplemental CO₂.

Cabomba furcata is often sold under the common name of “red Cabomba” or sometimes as C. piauhyensis. This extraordinarily beautiful species is another South American native, and is probably the most demanding species of all. Besides the strong reddish hue of this plant, it is readily identified in that it produces three finely pinnate leaves from each node, as opposed to the two produced by all other species. Like C. aquatica, it requires very strong illumination, soft water and supplemental CO₂. It also requires regular addition of iron supplements to maintain its red color. Even under conditions that seem near perfect, this plant fails to thrive in some aquariums.

Cardamine lyrata
Family: Brassicaceae

Cardamine lyrata is the only species of this genus of over 160 species that is commonly found in the aquarium hobby. This particular species is native to eastern Siberia, China, Japan and Korea. There are at least a couple of other species that do well under prolonged submersion, so it is possible that other species will find their way into the trade as time goes on. The genus is widely represented in temperate regions of the world, and even in the mountainous parts of the tropics.

Because Cardamine is a temperate climate plant, it usually does best in cooler aquariums. But it does reasonably well even at tropical aquarium temperatures as long as it receives plenty of light. It does better in water of at least moderate hardness, and often benefits from the addition of supplemental CO₂. Under favorable conditions it is a strong grower and reproduces very rapidly. In very warm water or in less than adequate light, the stems become spindly and the leaves smaller. Eventually, under these conditions, it often becomes spindly enough that it will need to be removed and replaced with fresh cuttings grown in cooler water.

The leaves of this dainty marsh plant are rounded to reniform (kidney shaped) with crenate margins. The leaves alternate on the delicate stems, and a lacy network of fine roots sprout from the base of many leaves. The result is a lovely, open, oriental look, reminiscent of dogwood branches. I think Cardamine lyrata is particularly attractive used in front of darker green plants with heavier foliage, such as large Echinodorus or Java fern. There, its lacy form and lighter green color are set off to best advantage.