Tree

A tree is a woody plant which has three principle characteristics: (a) the potential to grow to 20 ft (6.1 m) or more in height; (b) the formation of one or more trunks arising from the ground; and (c) the ability to stand on its own without support. Trees provide many products which are important to humans, such as timber, fruits, and nuts. They are also the dominant plants in the world's forests, and thus provide critical habitats for the other species which live there.

Most trees increase in thickness due to cell division in two special layers of undifferentiated tissues near the outside of their stems. This is known as secondary growth. The two tissues are referred to as the vascular cambium and the cork cambium. In contrast, herbs do not have secondary growth, and they stop growing once their primary tissues have matured.