It is estimated that there are just over 3 trillion mature trees in the world.A tree typically has many secondary branches supported clear of the ground by the trunk.
The three main parts of trees include the root, stem, and leaves; they are integral parts of the vascular system which interconnects all the living cells.
In trees and other plants that develop wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth.
Trees and forests provide a habitat for many species of animals and plants.
Tropical rainforests are among the most biodiverse habitats in the world.
In botany, a tree is a perennial plant with an elongated stem, or trunk, supporting branches and leaves in most species.
In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are usable as lumber or plants above a specified height.
Because of their longevity and usefulness, trees have always been revered, with sacred groves in various cultures, and they play a role in many of the world's mythologies.
Diagram of secondary growth in a eudicot or coniferous tree showing idealised vertical and horizontal sections.
Wood gives structural strength to the trunk of most types of tree; this supports the plant as it grows larger.