Geographical origin of aquarium plants.
When comparing aquarium fish and plants, it turns out that fish adapt much easier – some start breeding in captivity faster, others live more or less well, even if they do not breed in aquariums, whereas plants are much more delicate and sensitive. In experiments with chemical additives in water, plants were 10,000 times more sensitive than fish. Among hydrophytes, significantly more problematic species have been identified that not only refuse to breed, but even simply live in basins and aquariums. Neither the substrate suits them, nor the water, nor the light: they need water flow and level fluctuations. Hydrophytes turned out to be different – simple, medium complexity, and very difficult to keep. Therefore, it is so necessary to know their natural habitat conditions – biotopes – in order to create captive keeping conditions as close to them as possible.
1. Plants of SOUTH AMERICA – plants of the Amazon River. In the Amazon basin, the annual rainfall is very high, and precipitation is distributed unevenly here. This geographical region is characterized by two rainy seasons, between which dry periods are noted. In the upper reaches of the river (the Andean mountain region), dry periods are barely noticeable. In the bodies of water of South American virgin forests, where the aquarium plants of interest to us live, there are no permanent lakes and swamps, unlike the areas located near the Amazon and its large tributaries. Here, in the dense thickets, it is always very damp. The few water bodies are located 6-10 m above the normal river level and are flooded only during major floods. They are the homeland of the plants we are interested in.
The average annual air temperature is 25-26°C (from 14 to 40), water temperature is 28-30°C, in shallow water up to 40°C (from 18 to 32). Acidity in the western part of the Amazon is pH 6.2-7.0, in the central part pH 3.6-4.8, the central region of South America, Guiana, Brazil – pH 4.5-6.8. Therefore, plants are hardy, possess high adaptability, and are relatively easy to cultivate in aquarium conditions. During the rainy season, a stagnation occurs in the life of plants; after the flood ends, they begin to grow rapidly.
Numerous scientific studies undertaken in the 1950s mainly in the Amazonian aquatic system, based on the physical (coloration and turbidity) and chemical differences of many rivers, led to a conventional division of waters into three types. Based on their characteristic features, black, clear, and white waters are distinguished, between which, naturally, there are also many intermediate forms, which is why not every river or water body falls under this model.
Rivers with typically white water have clay-yellow, turbid waters and, unlike clear and black waters, contain a large amount of inorganic suspended matter, which settles along the riverbanks and forms exceptionally fertile soil. Examples of white-water rivers include the Rio Solimões, the Amazon, as well as the Yanayaku River in Peru and the Sepik River in Papua New Guinea. In contrast, rivers with clear water are poor in sedimentary impurities and have very clear water, ranging from yellowish-greenish to dark olive in color, which can be seen to a great depth. White sand beaches are often found on the banks. One of the most thoroughly studied clear-water rivers is the Rio Guaporé in southwestern Brazil.
The third group is formed by rivers whose water is clean, transparent, but distinguished by a dark brown color resulting from regular flooding of nearby forests. Humus is washed out in the process. Black water is extremely acidic and poor in dissolved mineral substances. Thanks to its interesting ichthyofauna, the Rio Negro (Brazil) is a very famous black-water river in fishkeeping. The basis for the formation of various water types is the properties of the soil, as well as climatic and landscape conditions.
Since there is a big difference between these three water categories regarding their physical, chemical, and biological properties, the character of the aquatic flora of the corresponding water type also differs. Black-water rivers create extremely unfavorable conditions for plants. These include the very acidic waters of many Amazonian rivers with a pH of 3.7 to 4.3, as well as a low bicarbonate content, where plants must make do with pure carbon dioxide as a nutrient. These properties exclude the development of a large number of aquatic plants in black waters. Only very few species have been able to adapt to such a habitat and are unable to exist in another environment.
Black-water rivers are found not only in Amazonia and Guyana, but also in many other countries around the world. All black-water rivers are characterized by significant flora poverty. For example, typical aquatic plants of the Rio Negro black waters are Cabomba aquatica, Utricularia foliosa, Azolla caroliniana, and various species of the family Podostemaceae; in Guyanese biotopes with pH values from 3.9 to 4.2, Mayaca fluviatilis and Tonina fluviatilis are occasionally found. But typical black water is also formed in Asian biotopes of certain Cryptocoryne species. One of the well-described places is the Tasek canal system on the Malacca Peninsula with Cryptocoryne purpurea.
Clear-water rivers exhibit an acidic environment, nevertheless with a pH of 4.6 to 6.6. The transparency of the water, which determines a favorable light climate, promotes the adaptability of plants to these conditions. Clear-water rivers are characterized as extremely poor in minerals and nutrients. But as the water analysis of the Rio Guaporé shows, there is nevertheless a complete and constant supply of nutrients that promotes a versatile life of the plant world in these waters depending on the season. The most important limiting factors for the distribution of aquatic plants are water level fluctuations.
White-water rivers have a very soft composition, but unlike black waters, they have a high content of dissolved minerals, which translates into high conductivity. White water has pH values ranging from slightly acidic to slightly alkaline, from 6.6 to 7.2. Although the nutrient richness of this water allows the development of many species, the significant growth-limiting factors are turbidity and low conductivity, as well as, depending on the season, water level fluctuations that usually reach several meters. Therefore, in most cases, submerged plants are absent in white water, and the vegetation consists of floating plants of the species Azolla and Ceratopteris, Eichhornia crassipes, Phyllanthus fluitans, Pistia stratiotes.
The Rio Guaporé River originates in the state of Mato Grosso (Brazil) near the border with Bolivia. Virgin forests still exist along the river. There, in the flood areas and river tributaries, the vegetation is exceptionally diverse. The upper reaches of the Rio Guaporé are white water. The average daily maximum of the warmest month (March) reaches 32.8°C and the average daily minimum of the coldest month (July) is only 14.6°C. Water analysis leads to the conclusion that the Rio Guaporé is a river with very soft, nutrient-poor water, in which, nevertheless, plants receive a sufficient amount of nutrients for growth.
Patches of dense vegetation are mainly found in bright and shallow places along the riverbanks, where sunlight penetrates intensively. The abundance of aquatic and marsh plant species in the vicinity of this river is unusually high. In addition to five species of Echinodorus, of which three belong to small and medium-sized species and two to large species, another 15 species of other genera were found, of which 11 grew in the river and 4 in the floodplain zones.
Floodplains of the Rio Sipao River (Venezuela). The Rio Sipao is a right tributary in the middle course of the Orinoco River. In its middle course, the river is swift and clay-turbid, but still forms small calm bays in many places, where dense thickets of Eichhornia diversifolia, Bacapa sp., and Tonina fluviatilis are found, growing knee-deep in water. Inhabited areas are located in the sun or slightly shaded by trees. The substrate is sandy, but in most cases covered with a thick layer of dead plant material.
Basin of the Rio Aro River (Venezuela). This refers to the swampy area of the Rio Aro River, a right tributary of the Orinoco. In standing water, approximately 30-50 cm deep, dense clumps of many aquatic and marsh plants grow – Cabomba furcata, Ludwigia inclinata, Bacopa reflexa, and Sagittaria sp. The substrate consists of brown clay. The water in this area was acidic, soft, and indicated fertilizer supersaturation.
Rio Yanayaku River (Peru). This is a right-bank tributary of the Ucayali River. Near the bank in slowly flowing water, a cover of floating plants was visible: Ceratopteris pteridoides, Ceratophyllum demersum, Ceratophyllum submersum, Eichhornia crassipes, Limnobium laevigatum, Ludwigia helminthorrhiza, Phyllanthus fluitans, Pistia stratiotes, Ricciocarpus natans, Salvinia auriculata, and Utricularia foliosa.
2. Plants of the INDO-MALAYAN ZONE – Malacca and Indonesia, New Guinea, Java, Sumatra, Kalimantan, Sulawesi. The climate is hot and humid. It is eternal summer here, with heavy rains throughout the year. There are no large rivers here; the terrain is impassable jungle with countless small water bodies – lakes and swamps. The average temperature is 25-27°C. Acidity pH 5.6-7.0. Most Cryptocoryne species grow in this region. They inhabit shady places, usually in water whose surface is completely covered with floating and other plants. Bacopa, Limnophila, and ferns grow in the channels and ditches. There is no pause in plant development. Plants cannot tolerate temperatures below 18°C.
Tasek Bera — a large wetland lowland with an area of about 60 km2 on the Malacca Peninsula in the southwest of Pahang State. It is intersected by canal-like watercourses and forms an impressive habitat for aquatic and marsh plants. Populations of Cryptocoryne purpurea, Blyxa aubertii, Barclaya motleyi, Eleocharis ochrostachys, Hydrilla verticillata, Ludwigia prostrata, Nymphoides indica, and Potamogeton wrightii are found there. The water is dark brown, very clear, and depending on the season has a transparency from one to two and a half meters. The water surface temperature fluctuates between 23 and 31°C. The water is very acidic and poor in minerals. The average pH is 5.33. The substrate is sandy, yet covered with a thick layer of peat mixed with undecomposed plant remains, wood, and silt. Under the influence of monsoon rains, the water level fluctuates significantly, reaching 5 m.
Sepik River (Papua New Guinea). A river several hundred meters wide with a fast current and clay-turbid water. Water analysis of this biotope shows that plants live in very soft water with low nutrient content and low conductivity. While the content of major plant nutrients – nitrogen and phosphorus – is low, a high concentration of zinc was noted.
3. Plants of INDIA, SRI LANKA, THAILAND, and VIETNAM. The eastern and southern regions of India, as well as the southwestern and southern parts of Sri Lanka, belong to the humid evergreen forest zone. The southern part of India is characterized by a monsoon climate. Therefore, in the summer period, rivers and lakes overflow their banks, forming a large number of additional water bodies. These water bodies are often connected to each other, so the chemical composition of the water depends to a very large extent on the amount of precipitation and the parent rocks of the water body. Seasonal fluctuations in water hardness and pH are quite significant.
Aquarium plants from the genera Lagenandra, Cryptocoryne, etc., are found in forest ponds and swamps overgrown with vegetation in the southern regions of India and Sri Lanka. The water surface is covered with water lily leaves and flowers, round floating leaves, and white fluffy flowers of the Indian floating heart (Nymphoides indica). Near the bank on the water surface, intertwined stems and bluish leaves of water hyacinth / Hydrorhisa aristata are visible. The space between these plants is occupied by clusters of the floating fern Salvinia (Salvinia). Where the water is not covered by floating vegetation, bright green leaves of Ottelia alismoides, semi-rolled into a wide funnel, reach upward from the bottom. This plant is widespread in the tropical and subtropical regions of Asia.
One of the main elements of these water bodies is the sun, and the illumination is such as we cannot even dream of in aquariums. Thus, we are not destined to see all the splendor of these plants in aquariums. A waterfall roars near the rocks, the water rushes swiftly; here the sand is clean, not silted, and well washed by streams. And it is here, in small clusters and individually, that bushes of yet another plant stand – Cryptocoryne thwaitesii. Its beautiful brownish-olive leaves are covered with dark transverse strokes on top, the underside is wine-red, and the edges are strongly wavy. The leaves are located at the water surface or rise slightly above it. Nearby, in calmer backwaters, are thickets of Cryptocoryne nevillii.
Here is another stream dweller – Aponogeton rigidifolius. Powerful roots are anchored in the sand, and the leaves on long petioles trail along the surface with the current. If seasonal climatic changes are small in the island’s tropical rainforest, they are clearly manifested in its higher eastern and northern regions. Here, water lilies, Cyperus species, and other Aponogeton species are characteristic of the water bodies. Thailand and Vietnam are located in the hot belt. These countries are characterized by a large number of swampy areas constantly nourished by tropical downpours. The water here is mostly soft and slightly acidic. Such aquarium plants as Cryptocoryne blassii, Cryptocoryne cordata, etc., grow in the water bodies. Acidity pH 5.8-7.3.
4. Plants of AFRICA. The change of natural zones in Africa occurs from the equator to the north and south depending on climate changes, especially changes in the thermal regime and precipitation amounts. African water bodies are mainly fed by rains and overflow significantly during this period, forming a large network of additional water bodies that are often interconnected. Inland water bodies are poor in mineral salts, and their waters are distinguished by hardness, especially in the lower parts of the runoff. Water bodies of evergreen tropical forests are heavily saturated with humic acids, and the active water reaction is often pH 5-5.4. The water is exceptionally soft; depending on the type of water body and the season of the year, its hardness ranges from 1.1 to 1.7, rarely up to 2.5. A huge number of various aquatic plants usually grow in backwaters and river floodplains.
In the areas where streams and rivers merge, a new biotope is formed. Such a phenomenon can most frequently be observed in the part of Nigeria called the central west. In the delta system, in shallow water and on the bank in muddy soil, huge thickets of aquatic and littoral plants are found. Water properties in the rivers here vary, as along their way they flow through diverse rocks, often through limestone. In such water bodies, water can have a pH of 7-8 and a hardness of up to 14°. Riverbeds are usually muddy or sandy, rarely lined with granite pebbles.
Aquatic plants can only occasionally be found in riverbeds. They usually grow in water bodies that are flooded only during major floods. When the water recedes, temporary lakes form on the surface, which gradually dry up. It is in them that amphibious plants usually grow. In Sudan, Senegal, Upper Volta, Togo, and Dahomey, the area of water bodies increases significantly during the rains. The water here usually has a pH of 6 and a hardness of 2-2.5°. Its level depends on the amount of precipitation.
All the above-mentioned West African biotopes are the homeland of aquarium plants: they usually grow along the banks of streams and rivers, often on moss-covered rocks, stones, and in impassable forests. Most of the year they rise above the water level and only during the rainy season are they submerged into the depths. Island of Madagascar. On the surface of standing water bodies, a familiar picture – dense thickets of water hyacinth and Pistia stratiotes. Let us approach one of the water bodies in the Ankazatòvo area. Near the bank in shallow water, thin green ribbons stretch toward the surface – something resembling the well-known Vallisneria. This is Aponogeton dioecus.
Further from the bank, where it is deeper, crimson wavy leaves adorn the underwater forest. They stretch from the depths to the surface, swaying quietly with the movement of the water. This is Ottelia ulvaefolia. Even further from the bank in our water body grow larger bushes – up to 1 m, also with wavy green leaves and also having received a similar specific name – Aponogeton ulvaceus. In underwater gardens, this plant is successfully kept and regularly blooms, easily reproducing by seeds and tuber division. And it is completely impossible to create suitable conditions in an underwater garden for such a unique plant as Hydrostachys pinnatifolia. Among the stones, in the swift current of the waterfall, thick feather-like leaves trail in the flow.
River biotope of Madagascar. Aponogeton madagascariensis has long been indisputably one of the most popular aquarium plants. This biotope is located about a kilometer from the village of Beforona on the river of the same name, at an altitude of 900 m. The narrow-leaved Aponogeton madagascariensis plants grew in slightly turbid water at knee depth with a strong current, with the leaves barely reaching the water surface. The substrate consisted of very clayey sand mixed with gravel, large stones, and rock fragments. The brown color of the leaves indicates that the plants in natural conditions grew under stronger illumination than in a cultivated environment, because specimens brought from there subsequently developed only olive-green leaves in the aquarium. The water level at this place drops so much during the dry period that the leaves of Aponogeton madagascariensis trail along the surface.
Environmental factors, Seasonal influences and water body types.
Plants rooting in the substrate. Floating on the surface, in the water column. 
