All About Leaves

All About Leaves

By Madison Nef

Leaves are a very vital part of the tree. All leaves, while seemingly small, unimportant and just for décor… are responsible for producing all the food in the tree. Each leaf is like a small, green, natural factory that creates food for the rest of the tree. All leaves look different and are unique, like thumbprints. No leaf is the same as another leaf.

Depending on the type of tree, a leaf will look different. They are broad a blade-like, and come in many different sizes, shapes and colors. Their edges can be smooth or have small, jagged ridges called teeth. Looking at a leaf, the first thing you will notice about it is its shape. This can help you identify what kind of tree it’s from.

When describing leaf shapes, scientists use specific terminology to name them and tell them apart from each other. Here are the nine most common scientific names for leaf shapes:

     Linear

     Ovate

     Lanceolate

     Elliptic

     Deltoid

     Bipinnate

     Palmate

     Palmatifid

     Pinnate

Leaves are divided into these different categories by their structure. A leaf with just one blade is classified as ‘simple’. A leaf with many different blades is classified as ‘compound’, which breaks the leaves down into two categories- pinnate and palmate. Leaves of deciduous trees are often times flat and wide, while the leaves from conifer (evergreen and cone-bearing trees) are needle-like.

Deciduous are trees like oak and maple, which lose their leaves in the fall every year.

Conifer trees are evergreens, such as pine and spruce, that keep their leaves year-round.

With this out of the way… how, then, would you classify holly, boxwood, and rhododendron? These leaves are broad and flat like deciduous trees, but keep their leaves green and strong all year. These types of plants are called broadleaf evergreens, because they keep their leaves green and for many seasons.

And what about larch and cypress trees? These deciduous conifer trees, as they are called, have leaves like a conifer tree, but lose all of their needles in the winter.

Leaves are responsible for a lot: they give the tree food, shade food that the tree grows, and shade and keep the tree cool itself. Let’s look at the outside morphology of a leaf:

The blade is the broad, flat part of the leaf. The blade can be shiny, smooth, fuzzy, or dull. The top and bottom of the blade can be and often are different colors and shades.

The leaf margins, or the outer edges of the leaves, can be extremely smooth OR have jagged teeth or rounded lobes on the edge (as mentioned above).

The apex is the very tip of the leaf. The apex can be rounded, indented, or pointed- it all depends on the type of tree.

The petiole, or leaf stem, is what supports and connects the leaf to the tree. The petiole is a channel for the food and water that the tree AND the leaf both need to grow and survive.

These petioles can also bend so that the leaf gets all the sun it needs- something essential for the food-creating process. The stem also allows the leaf to bend the correct way in high winds to avoid damage.

Stipules are small leaf-like structures that form around the leaf as it begins to develop to protect it. For example, willow stipules actually produce a bug repellant so that bugs don’t damage the growing leaves.

The midrib is the center vein that runs down the center of most leaves. Pinnate, or feather-like leaves all have this midrib, with smaller veins that branch out on either side of it. Palmate leaves just have veins that spread out from the base of the stem.