The Tropics Of The Indomalayan Area

Together with the South American tropics, this area produces more aquarium plants than any other area. Most aquarium plants (and fish) from the Indo-Malayan area originate from the Malayan peninsula and Indonesia (especially the larger islands of Java and Sumatra), Borneo, the Celebes, and New Guinea. A great number of species also come from Ceylon (Sri Lanka).

The most conspicuous feature of the area is the absence of large rivers. In the places where, because of thorough drainage, no rice fields have been cleared, the whole country is covered with impenetrable jungle interspaced with small lakes, rivers, and marshes. Two factors, the land being covered by dense vegetation plus the proximity of the sea, influence the nearly constant temperature which varies only slightly from 77° to 81° F (25° to 27° C). During the changing seasons of the year as well as during the day, the temperature varies so slightly that an almost constant annual temperature may be said to reach a substantially higher value than the temperature of tropical aquariums in the home.

The greater part of the Indo-Malayan area is very rainy (25 to 40 meters rainfall per year). Though the rains are distributed over two periods, no distinct dry period occurs (except in the eastern

A typical rural scene in Thailand. In this kind of habitat the environmental conditions do not change very much throughout the year. Photo by Dr. H.R, Axelrod.

part of Indonesia), so the waters have no periodic variations in conditions and in the jungle there are many permanent water reservoirs of large and small size. Only in very shallow pools and in marsh formations does the depth of water vary sufficiently to be able to influence the composition of both aquatic and amphibious vegetation.

The flooding in'this tropical area is not caused simply by rising river waters, but during the rainy periods an excess of water is present everywhere and increases evenly. Afterward the height of the water level decreases evenly. The aquatic vegetation is therefore not damaged by a wild current and the cycle of development is distinct in the numerous species of amphibious plants.

Although a great number of species of water plants come from the Indo-Malayan area, the most typical of them are the Ara-ceae, particularly the cryptocorynes. The typically submersed species (Cryptocoryne affinis, C. siamemis, C, cordata, etc.) grow in

Plants Found Indo Malayan

A typical site In a rubber plantation in Indo-Malaysia where Cryptocoryne cordata is found growing in the irrigation canals.

permanent, often very deep, waters and can flower throughout the year, although in waters deeper than 30 to 40 cm they do not flower but are propagated vegetatively. In such cases the cycle of development is not typical.

Amphibious species (C. hecketii, C. walkeri, C. nevillii, C. lucens) are submersed during the rainy period, when there is a stage of vegetative propagation by runners from the rhizome. If the water level falls they pass into the emersed way of life, when they flower and produce seeds. These species are typically plants of the jungle formations. They grow in semi-shaded conditions under several layers of luxuriant forest growth, often in water where the surface is quite covered with floating plants.

Other aquatic Indo-Malayan plants such as Limnophila, Ceratopteris, and Bacopa are found in artificial and natural channels which connect the lagoons and small lakes.

In summary, the Indo-Malayan species of plants are characterized by a medium which offers them an unvarying.and relatively high temperature, about 79° to 83° F (26° to 28° C), for both air and water. The aquatic vegetation consists of amphibious spe-

A mass of amphibious vegetation growing along a river bank in Bangkok, Thailand. These plants are rarely completely inundated except, perhaps, during extreme high water as a result of a typhoon. Photo by Dr. H.R. Axelrod.

cies (Lagenandra, some CryptocoTyne species, Limnophila) as well as typically submersed species (some Cryptocoryne species, Myrio-phyllum). They have no period of vegetative rest» but some amphibious species, in accordance with the period, are capable of vegetative growth and propagation as well as a flowering stage with the consequent production of seeds.

The plants of this area are, therefore, more exacting in their requirements. They are sensitive to fluctuation in temperature, especially to serious drops which for extraordinarily delicate species may be deadly even at 65° F (18° C). Other plants may succumb at about 59° F (15° C). It is essential to give Indo-Malayan plants temperatures of 77° to 80° F (25° to 27° C) throughout the year.

Some cryptocorynes can be induced to flower only with great difficulty. Even though a sufficient number of experiments has not yet been undertaken along this line, it can be presumed that in artificial cultures it is necessary to adhere to the normal cycle of development if blossoming is to be encouraged: the change from emersed to submersed growth and back again must be duplicated by a regular fluctuation of the water level.

According to notes on herbarium sheets and detailed observations by Prof. Schulze (1967 and 1971), aquatic plants in the Indo-Malayan area (particularly Cryptocoryne) grow within three main biotopes.

1) Banks of strong rivers up to 10 to 100 km from the mouth. The cryptocorynes grow in well lit or only slightly shaded areas up to 50 meters above sea level. Under these conditions are found all the species preferring the terrestrial way of life. They are nearly always found in shallow waters, the leaves and inflorescences growing above the level of the water, as in the case of C. ciliata. These species are often found along strong streams penetrating deep into the woods, but wider streams may have more vegetation on their banks because of increased illumination. These species do not grow in association with Lagenandra and Hygrophila because they do not occur in river beds. Other species of the genus Cryptocoryne also are not found in river beds with such a biotope. The aquatic vegetation is represented chiefly by Aponogeton rigidifo-lius, Myriophyllum spp., HydriUa verticillata, Blyxa, and Potamogeton species. The submersed form of Crinum thaianum joins this typically Malayan flora in Thailand. In Sarawak C. ciliata occurs with C. lingua and C. pontederiifolia var. sarawacensis; these species often descend right into the beds of rivers together with Spr-claya mottleyi. In spite of the nearness to the sea, C. ciliata grows mostly in the areas with fresh water. It is rarely found in areas with brackish water.

2) Small streams up to 2 to 10 meters wide and under normal circumstances quite shallow (10 to 30 cm), with the surface rising to 1 or 2 meters after heavy rains. These brooks are found in thickly wooded and shaded areas, usually in elevations of 50 to 100 meters in Ceylon (rarely to 500 meters) and 1200 meters in northeastern India. The main characteristic of these biotopes is crystal clear water with a pH of about 6 to 6.5, and mainly soft rainwater. The bed of the brooks is rocky or stony and covered with a sand-silt mixture brought down by running water from higher elevations. The cryptocorynes occur mainly in cultures of single species on overgrown river beds and are exposed to the conditions of amphibious life. Depending on the rainfall, the depth of the water often

Cryptocoryne Diversen

A newly collected Cryptocoryne plant from its natural habitat in Thailand Photo by Dr. H.R. Axelrod.

varies within a few days from 1 to 2 meters to a few centimeters, In such conditions C. balansae grows in Thailand, C. wendtii and C. axelrodii in Ceylon, and C. bullosa in Sarawak. In the case of lowland species living at 25 to 100 meters above sea level, C, nevillii and C. becketii ascend to the limit of 500 meters in Ceylon, and C. crispatula was found up to the height of 1200 meters in northeastern India.

3) Marshes of primeval forests, tidal mangroves, irrigation canals of rubber plantations, and stagnant waters. The beds of these localities are usually soft, either muddy or of sandy clay. The water is crystal clear and slow moving, usually neutral or a little acid. Only during rainfall are these areas flooded with thick layers of mud and the water becomes tinted brown, which temporarily lowers the pH, Cryptocoryne cordata as well as C. lingua, C. gracilis, and other species grow mainly under these conditions.

Plants in nature are exposed to some environmental conditions which can be duplicated in the aquarium only with difficulty. An aquarium is only a small water reservoir into which only a few plant species can be planted. These species may come from diverse parts of the world and are quite unrelated to each other. Yet the dissimilarity of plants in natural locations is nullified by the fact that there is the same depth of water all year, and usually also the same temperature and other physical and chemical conditions. As a rule only the duration and intensity of the light vary.

In the aquarium other changing conditions appear, conditions that are unknown in nature. In nature the least variable part of the habitat is the soil, while in the aquarium it is very variable. If the bottom is enriched with organic substances (peat, humus, etc.) they will influence the composition of the water and may themselves undergo anaerobic decomposition. Consequently poisonous gases arise to adversely affect the medium. Thus the advantage of using clean sand which is gradually enriched from normal decomposition of plant and animal wastes.

In natural aquatic plant communities there is generally a characteristic biological balance. In accordance with the depth of the water, the temperature, illumination, etc., some species develop only in certain seasons of the year, later to die and give place to others. The species composition therefore changes with the period of vegetative growth and the period of flowering. This does not occur in the aquarium.

The main reason for the disturbance of the biological balance is the fact that conditions in the aquarium change but little during the year. The community is not subject to the proper cycle of development, but the species for which the conditions of a certain aquarium are most favorable thrive to the detriment of plants not so favored. The species which propagate vegetatively repress the plants propagated only by seeds. In darker aquariums the members of the genus Cryptocoryne will prevail and make the growth of Echinodarus and Vallimeria impossible; in lighter aquariums the reverse occurs.

The interaction between the separate species of plants is therefore much stronger in the aquarium than in nature. After a while it is generally necessary to make certain changes in the aquarium such as thinning out the overly abundant species, removing shade plants, and regulating the amount of floating vegetation.

The facts that the amount of water in the aquarium is relatively small and that changes take place (although slowly) mean that various species of plant influence each other chemically by acting upon the properties of the water. For example, Cryptocoryne species tend to acidify water while Vallimeria species tend to alkalize it. This causes a mutual intolerance between some spe-

Enormous amounts of silt from surrounding higher ground account for the brown color of this tributary of the Amazon River at Tefe, Brazil. Photo by Dr. Herbert R. Axelrod.

A great mass of water plants growing under water In the very clear waters of the Paranajuba River, Upper Xingu, Brazil. Photo by Harald Schultz.

Valtisneria is best maintained with those plant species that tolerate alkaline conditions. It can also be utilized alone as seen in this set-up. Photo by Dr. Herbert Ft. Axelrod.

cies of aquarium plants, which sometimes becomes much more evident in the aquarium than in nature.

It goes without saying that this intolerance does not arise where the aquarium is planted with a greater number of species. It may, however, appear in those aquariums where Cryptocoryne plus Vallisneria or Cryptocaryne plus Sagittaria combinations form a substantial part of the vegetation. In darker aquariums the growth of Cryptocoryne species will predominate, which will influence the reaction of the water because they will acidify it and thereby further inhibit the development of the Sagittaria or Vallisneria, eventually arresting their growth. In brightly lighted aquariums there are better initial conditions for the development of the latter two genera, which will regulate the reaction of the water toward the neutral point or will alkalize it slightly, inhibiting any further development of cryptocorynes.

In summary, we have seen that the aquarium is mainly a sector of shallow to moderately deep bankside waters and cannot support the diverse forms of vegetation that are present in various depths and on bankside fringes in nature. Thus it is ideal to complement an indoor aquarium with appropriate containers of various sizes in which shallows covered with floating vegetation can be maintained and where a number of marsh and amphibious flowering and non-flowering plants can be cultivated.

In this aquarium set-up the tall and more robust plants are confined to the background, while the low vegetation is limited to the front part. The bushy-leaved plants provide some contrast to the broad-leaved forms.

In this aquarium set-up the tall and more robust plants are confined to the background, while the low vegetation is limited to the front part. The bushy-leaved plants provide some contrast to the broad-leaved forms.

Terrestrial plants ¡trees) and aquatic plants (floating and emersed) are seen growing together in this area of the Amazon River at Tefe, Brazil. Photo by Or. Herbert R. Axeirod.

Glossadelphus zollengeri is an aquatic moss from Java and Celebes. The small black and white photo shows a part of the plant In detail. Photo by Dr. D. Terver.

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