Most forests contain a mixture of many different species of trees, and rain forests contain the most species of all. Both coniferous (cone-bearing) and nonconiferous evergreen trees exist within their boundaries. However, because most rain forests are difficult for humans to penetrate and usually are found in countries that cannot afford to fund scientific studies, and may not want foreign scientists working there, only a handful of these species have been named.

The trees and smaller plants in a rain forest grow to different heights, forming "layers." The crowns of tall trees create a canopy, or roof, over the rest of the vegetation that is typically at least 131 feet (40 meters) above the ground. Here and there, the very tallest trees, called emergents, pop through the canopy like lonely towers. Because the trees grow so close together, they help support one another. Beneath the canopy grows at...