The two basic kinds of trees are coniferous and deciduous, which branch into a variety of types and species. The exact number of tree species in the world is undetermined because only a small percentage of plant or animal species have been discovered and classified.
Trees are so varied that, as of 2013, the Amazon rain forest, also known as Amazonia, is estimated to hold nearly 16,000 species of trees. For commercial purposes, trees are normally determined by the quality and density of the wood they provide, such as hardwoods and softwoods. Trees play an important role in maintaining a healthy ecosystem.