Anatomy and Biology of a Tree Leaf

Cellular Structure of a Tree Leaf

Leaves are food factories for the tree. Powered by sunlight, the green substance in leaves called chlorophyll, use carbon dioxide and water to produce life-sustaining carbohydrates (sugars). The entire process is called photosynthesis.

A tree's leaves are also responsible for the twin functions of respiration and transpiration. Both of these processes support evapotranspiration which allows the tree to move water and nutrients up from the roots.

Through small openings on the leaf, called stomata, a tree can regulate moisture and gasses. With the exchange of water and the absorption of carbon dioxide during the process of photosynthesis, the release of life-sustaining oxygen occurs as a by-product.

Internal Tree Leaf Structures

The leaf blade is composed of tissue layers, each having an important part to play in a functioning leaf. Find these structures on the attached diagram of cellular leaf tissues.

Epidermis – The leaf's outer layer and protective "skin" surrounding leaf tissues.

Cuticle – A waxy protective coating on the leaf epidermis that prevents water loss on leaves, green stems, and fruits.

Leaf hairs – Coverings on a leaf's epidermis that may or may not exist with every tree species.

Palisade layer – A tightly packed layer of long tube-like parenchyma tissues filled with chloroplasts for photosynthesis.

Chloroplasts – Sub-cellular, photosynthetic structures in leaves and other green tissues. Chloroplasts contain chlorophyll, a green plant pigment that captures the energy in light and begins the transformation of that energy into sugars.

Vascular bundle – Xylem and phloem tissues, commonly known as leaf veins.

Spongy mesophyll – Layer of parenchyma tissues loosely arranged to facilitate movement of oxygen, carbon dioxide, and water vapor. It also may contain some chloroplasts.

Stomata – Natural openings in leaves and herbaceous stems that allow for gas exchange (water vapor, carbon dioxide and oxygen).

Guard cells – Specialized kidney-shaped cells that open and close the stomata.

Using Leaf Anatomy to Identify a Tree Leaf

Botanical Structures on a Leaf

A tree's leaf is the best major botanical marker that helps in keying out and identifying any species of tree that has a leaf. Most trees can be identified by the leaf alone - they are unique! Tree Leaves come in many shapes and sizes, many with similar structures but most with subtle differences. Even slight differences can determine an exact tree species identification.

True leaves are blade-like and have a connection to the twig called a stalk or petiole. The edges of all leaves are called margins and can be smooth or toothed but can also be entire (without lobes) or with a lobe and a sinus.

A Tree leaf can be symmetric or asymmetric off the midrib or midvein. A leaf can have a single midrib or several radiating off the stalk. A leaf will have veins radiating off these midrib(s).

Using these Structures to Identify a Tree

The most popular and easiest method to identify a tree is to use a tree leaf identification key. Most tree identification guides depend heavily on using the leaf as a starting point. I have also developed a quick way to ID the most common trees in North America - Tree Identification Using a Tree Leaf Key.