Tree Anatomy: the parts of trees and their functions

First, we will look at the overall tree anatomy. Then, we will peak inside the tree to examine the layers of a tree’s trunk and their functions.

Overall Tree Anatomy

We can think of trees as having three main parts. Let’s take a look at each.

Roots are the underground parts of a tree that takes up water and dissolved minerals. They also help anchor the tree to the soil.
The trunk is the main woody stalk of a tree which supports all other branches.
The crown is the top portion of a tree. It includes the branches and leaves or needles extending from the main trunk. The crown of a tree will look quite different in different types of trees. Picture the crown of a deciduous tree, conifer tree, or palm tree. Let’s take a closer look at the parts of the crown:
- A branch is any woody stalk extending from the main trunk.
- The leaves are parts of a tree that produce the tree’s food through photosynthesis. In deciduous trees, leaves are broad and flat, and fall off the tree at the end of each growing season.
- The needles are the leaves of a coniferous tree, which produce the tree’s food through photosynthesis. Needles do the same job as broad flat leaves but stay attached to the tree throughout the entire year.

low angle shot photography of green trees

Tree Trunk Anatomy

Inside of a human body, you will find different organs: a heart, intestines, lungs, kidneys, etc. Just like humans, trees have different organs inside their trunks too. The trunk of a tree is made up of several layers, each performing a different function. Let’s take a look.

The anatomy of a tree trunk coloring activity for kids to learn about tree science

Bark is the rough, protective outer coating. Bark helps protect the tree from insect and fungi invaders.
The phloem underlies the bark. The phloem’s function is to transport sugars. Sugars form in the leaves during photosynthesis, and the phloem moves the sugars to other parts of the plant where they are needed for growth.
The cambium is a thin layer of dividing cells between the xylem and phloem. This is where secondary (outward) growth occurs. In temperate climates, the most growth happens during the summer. This is why tree rings form.
The sapwood underlies the cambium. The sapwood is the living part of the xylem, which actively moves water upwards through the tree. Water is drawn up through the ground via the tree’s roots. Water leaves the tree through tiny pores called stomata in the leaves, in a process called transpiration. The xylem grows from the cambium – we can see tree rings in the xylem.
The heartwood is old, inactive xylem tissue. Heartwood no longer has living cells and does not move water. Heartwood provides structural support. Both living and dead xylem parts (sapwood and heartwood) contain tree rings that formed each year as the tree grew inwards from the cambium.
The pith is at the very center of the tree trunk and plays a role in the movement of nutrients. In older trees the pith is often very tiny or diminished, relative to the size of the heartwood.