South America possesses a distinctive plant life. The biotic region is called the Neotropics, and its faunal realm the Neogaean. This region extends southward from the Tropic of Cancer and includes Central and South America—even the temperate southern portion. There are some similarities between South America’s vegetation and that of other continents, as a result of past geologic developments. The pattern of distribution within the continent is complex because of the variety of climatic and ecological zones. The northern tropical regions are the richest in diversity, while the southern regions and the western Andean highlands are much impoverished, despite some differentiation.
Grasslands are abundant in the South American lowlands. They can be classified as tropical, as with savannas, or subtropical, as with the Argentine Pampas.
Tropical savannas are found mostly in the Llanos of Venezuela and northeastern Colombia. These vast plains are covered with grasses and sedges, but tree clusters (mainly palms) also grow, especially along streams.
The flat or softly rolling plains called Pampas, which constitute the greater part of eastern Argentina, are covered with grasses. It is believed that the Pampas were originally covered with trees but that the trees were removed by humans. Others think that the plains were always covered with grassy vegetation, citing the existence of the ombu, a scrubby treelike plant that is part of the grass family, as an example. Exotic pines, eucalypti, oaks, and poplars constitute introduced trees. To the south the Pampas merge with the Patagonian steppe, where tussock grasses are mixed with scattered low bushes and spiny plants.
The proportion of endemic plants in South America is very high, even at the family level. Among angiosperms (plants having seeds enclosed in an ovary) no fewer than 25 families and 3,500 genera are endemic to the tropical and temperate zones.
Others are related to African plants or belong to southern plant groups also distributed in southern Africa and in Australasia. Vegetation is by no means uniform throughout the continent; its distribution is determined by climatic, geographic, soil, and sometimes anthropic (human-related) differences.
Rain forest covers the largest part of the Amazon region, most of the Guianas, southern and eastern Venezuela, the Atlantic slopes of the Brazilian Highlands, and the Pacific coast of Colombia and northern Ecuador. The Amazon region is the largest and probably the oldest forest area in the world; it also ascends the slopes of the Andes until it merges with subtropical and temperate regions. On its southern border it mixes with the woodlands of the Brazilian state of Mato Grosso, with galleries of trees extending along the rivers. Consisting of enormous trees, some exceeding a height of 300 feet, the rain forest is composed of an almost incredible number of species growing side by side in the greatest profusion and arranged in different strata. There are about 2,500 species of Amazonian trees. In the region of Manaus, Braz., for example, 1,652 plants belonging to 107 species in 37 different families were found on about 1,900 square feet.
The forests of the swamps (igapós), where the ground is inundated or very marshy throughout the year, cover the lowlands. Characteristic trees are, among others, jacareúbas(Calophyllum brasiliense), which is a tall tree with hard reddish brown wood used for heavy construction, araparis.
In the annually flooded plains known as várzeas, trees are higher and quite diversified; they include oeiranas (Alchornea castaneifolia), a euphorbia (i.e., characterized by a milky juice), and the trumpet tree (Cecropia peltata), a rapid-growing tree of the mulberry family with a light wood. Palms and hevea (wild rubber plants) grow in these forests. The forests of the nonswampy areas are rich in hardwoods, of which acapu (a tree with dark brown wood), pau-amarelo (Euxylophora paraensis), pau-santo (Zollernia paraensis), massaranduba (a Brazilian tree with light reddish brown wood), jarana (a tree with hard, heavy, durable wood), and matamata (a tree with hard, heavy, durable wood, used for pilings) are the best known. Hevea and the Brazil nut tree (Bertholletia excelsa) are characteristic of these forests where spiny palms cover the ground. Epiphytes (nonparasitic plants that grow on other plants, deriving moisture and nutrients from rain and air) are numerous, mostly Bromeliaceae (a family having spiny leaves), orchids, and ferns. Lianas abound, particularly in drier forests. "South America" © Emmanuel BUCHOT, Encarta, Wikipedia
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