South America
Introduction
The continent of South America has about one-eighth of the Earth's land surface, situated between latitudes 12°N-55°S and longitudes 80°-35°W; no other continent has a greater latitudinal span. Eighty percent of its land mass is within the tropical zone, yet it extends into the subantarctic. The extensive zones of temperate and cold climates in the vicinity of the Equator, in the Andes, are unique. The land area of about 17,519,900-17,529,250 km² is under the jurisdiction of 13 countries (Table 49); French Guiana is governed as an overseas department of France. The region's 1995 population of c. 320 million people is estimated to reach 452 million people in 2025. Three of the world's 21 megacities are in South America: São Paulo, Buenos Aires and Rio de Janeiro (WRI, UNEP and UNDP 1994).
Geological setting
Although the neotropics may be conveniently considered as a single phytogeographic unit, the region is geologically complex. The neotropics include not only the South American continental plate but the southern portion of the North American plate, as well as the independent Caribbean plate (Clapperton 1993). The complicated geological history of the region, for example as these plates intermittently separated and collided through the Cretaceous and the Tertiary, provides the milieu within which plant evolution has been superimposed.
South America has been an island continent during most of the period of angiosperm evolution, whereas Central America constitutes one of the two tropical parts of the Laurasian "world continent". Both South America and North America have been moving westward, roughly in tandem, since the breakup of Pangaea in the Mesozoic. In contrast, the Antillean plate with its flotsam of Antillean islands formed only during the Cenozoic and has moved in a retrograde eastern direction, at least with respect to its larger neighbours. Whereas South America and North America have been widely separated through most of their geological
The continent of South America has about one-eighth of the Earth's land surface, situated between latitudes 12°N-55°S and longitudes 80°-35°W; no other continent has a greater latitudinal span. Eighty percent of its land mass is within the tropical zone, yet it extends into the subantarctic. The extensive zones of temperate and cold climates in the vicinity of the Equator, in the Andes, are unique. The land area of about 17,519,900-17,529,250 km² is under the jurisdiction of 13 countries (Table 49); French Guiana is governed as an overseas department of France. The region's 1995 population of c. 320 million people is estimated to reach 452 million people in 2025. Three of the world's 21 megacities are in South America: São Paulo, Buenos Aires and Rio de Janeiro (WRI, UNEP and UNDP 1994).
Geological setting
Although the neotropics may be conveniently considered as a single phytogeographic unit, the region is geologically complex. The neotropics include not only the South American continental plate but the southern portion of the North American plate, as well as the independent Caribbean plate (Clapperton 1993). The complicated geological history of the region, for example as these plates intermittently separated and collided through the Cretaceous and the Tertiary, provides the milieu within which plant evolution has been superimposed.
South America has been an island continent during most of the period of angiosperm evolution, whereas Central America constitutes one of the two tropical parts of the Laurasian "world continent". Both South America and North America have been moving westward, roughly in tandem, since the breakup of Pangaea in the Mesozoic. In contrast, the Antillean plate with its flotsam of Antillean islands formed only during the Cenozoic and has moved in a retrograde eastern direction, at least with respect to its larger neighbours. Whereas South America and North America have been widely separated through most of their geological