AQUATIC HORTICULTURE		BY KAREN RANDALL

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More of the “Cs”

Although there is only a single genus in the family Ceratophyllaceae, it is one of the most successful genera and can be found almost worldwide. Known as hornwort in the aquarium hobby, Ceratophyllum has long been a favorite among fish breeders. Its fine leaves provide perfect fry cover in livebearer tanks and spawning media for egg scatterers.

Ceratophyllum is a completely rootless plant, although it is capable of using modified lower leaves to anchor itself into the substrate, both in the wild and in the aquarium. The stems are long and slender, easily growing to 6 feet or more in length if not cut back regularly. Both the stems and leaves are brittle and quite fragile, allowing broken plant fragments to float free and colonize other areas in the wild. Hornwort branches freely, producing large bushy masses.

In tropical climates, the plants grow year round. In temperate climates, they sink to the bottom as cold weather approaches. There they produce dense short growth, which will wait out the winter and quickly regrow when the water warms in the springtime. Because the plant is found in both warm and cold climates, it is a good candidate for cool water tanks as well as tropical.

Ceratophyllum produces tiny, inconspicuous flowers under the surface of the water. The pollen of these plants is specifically designed to be spread by water currents. While the plants do reproduce sexually, the predominant method of propagation is vegetative. Even a very small piece is capable of growing into a new plant.

This has been a problem in many areas, where even a small piece of plant material stuck on a propeller or boat trailer can carry the plants into a new body of water. Here they can quickly reach pest proportions, choking waterways and, occasionally, even drowning water fowl that become entangled in the thick mats of vegetation.

In the aquarium, however, this vigorous growth can be put to good use. Ceratophyllum thrives in hard water, and will also do quite well in softer water. It can be left to float free or can be anchored in the substrate, depending on the wishes of the aquarist, and will tolerate fairly low light levels — more reasons that it makes an excellent choice for a beginner's tank. If the plant has a fault, it is that it is such a vigorous grower that it can completely block light to lower sections of the tank if it is not cut back regularly.

The fact that it does grow at the surface and grows so quickly make it an excellent choice as shade, and as a “nutrient sponge” in tanks that are experiencing algae problems. Some sources say that hornwort also produces allelochemicals that act directly against algae. Either way, it is a useful plant in the battle against algae!

One warning about medications in a tank containing Ceratophyllum. This plant is copper sensitive, so copper-based medications should not be used. The plants will quickly shed all their leaves when exposed to copper and make a huge mess in the tank.

There are two species of hornwort offered in the aquarium trade. The first is Ceratophyllum demersum, which produces coarser leaves, and C. submersum, which is much finer in texture. There is also an attractive form of C. demersum from Mexico. This variety has red stems, which contrast nicely with the dark-green foliage.

Crassula
Family: Crassulaceae

Crassulaceae is an interesting family in that the plants are succulents — the plants can store water within their tissues and are adapted for an arid environment. There are 35 genera and about 1500 species in the family, and, in spite of the fact that many live in dry areas of the world, there is one genus, Crassula, that contains some species adapted to marsh and aquatic habitats. There are approximately 300 known species in the genus and even among these there are only about 10 adapted to wet conditions. The genus is found almost worldwide, although there is a preponderance of species in the southern parts of Africa.

While some of the other species might prove to be useful aquarium plants, the species most likely to be found commercially at this point is Crassula helmsii, a native of Australia and New Guinea. This is a lovely light-green plant with thick, fleshy, needle-shaped leaves. It requires strong light, but is otherwise undemanding. It is at its best when allowed to grow into a dense cluster, in which form it is a beautiful accent set in front of dark colored larger-leaved plants.

Crassula will flower if allowed to grow emersed. The flowers are small and pale pinkish white with three to five petals. While certainly not large enough to be show stoppers, they are quite attractive. Propagation is usually through cuttings, which grow rapidly under good conditions. For even more rapid growth, the plants can be grown emersed, in very wet substrate.

Crinum
Family: Amaryllidaceae (Narcissus family)

Crinum is the only genus in this widespread family that contains aquatic species. These are the plants that are commonly sold to aquarists under the common name of “onion plant.” This name has been given to the plants because of the large, onion-shaped bulb at the base of the plant. From there, the plants produce long, strap-like leaves. One useful thing about the plants in this genus is that they seem to be unpalatable to herbivorous fishes, which usually leave them alone.

The most commonly sold Crinum is C. thaianum, a species native to Thailand. With leaves that can reach up to 3 meters (almost 10 feet!) in length, this is a plant really suited to only the very largest tanks. The leaves are bright green and flat, with a look similar to giant Vallisneria. Even then young plants are easier to keep in check. The leaves can grow very rapidly under good conditions, and can actually wrap around the perimeter of the water surface in the tank.

Other than the size requirements C. thaianum is not a difficult plant to care for. It does best with moderately strong illumination, but tolerates a wide range of water conditions. When planting the bulb, make sure that at least 1/3 of the bulb remains above the surface of the substrate or it may begin to rot. Under very favorable conditions, the plant has been known to flower in the aquarium, producing a lovely lily-like flower. Propagation is via bulb offsets from the base, but is not commonly seen under aquarium culture.

Crinum natans is another species that can be encountered in the hobby. This plant stays slightly smaller than C. thaianum, and the heavily ruffled, very dark green leaves are very attractive. Culture is the same as for the previous species.

The last Crinum that is occasionally seen for sale is C. calamistratum. The leaves are dark green and very narrow with tightly ruffled margins. This plant is the smallest of the group, although still suitable only for fairly large tanks. The bulb of C. calamistratum is correspondingly smaller than the other species mentioned, but this species is more likely to produce offsets. C. calamistratum will tolerate more salt in the water than many species, so it is a good candidate for the brackish tank.