Identifying Plants: Leaves Part I

Here we are going to discuss the parts of a leaf and leaf arrangements to help understand the lingo used to identify plants.

Identifying Plants- Leaves Part I

Let’s start with the parts of the leaf.

Parts of a Leaf I

Blade: Flat part of the leaf where photosynthesis occurs

Petiole: Part of the plant that joins the leaf to the stem or twig

Vein: Provides support for the blade as well as transporting food and water

Midrib: Large, central vein that starts at the base of the blade and extends to the tip

Margin: The edge of the leaf

Node: (not labeled) The area that the leaf grows from on the stem or twig

Leaf Arrangements on the Stem

Leaves are arranged in a few different ways. These are the two most common.

Alternate

Alternate arrangements consist of leaves that are in an alternating pattern on the stem or twig.

alternate leaves

Opposite

Opposite arrangements consist of leaves that are opposite of each other on the stem or twig.

Opposite Leaf Examples

 

Leaf Arrangements

It’s important to first note that leaves start at the node. From the node, the petiole may have one or more leaf growing from it.

Simple Leaves

Simples leaves are a singular leaf attached to the petiole.

Simple leaf

Compound Leaves

Compound leaves have more than one leaf attached to the petiole. These leaves are actually called leaflets and the leaf itself starts at the node.

There are three kinds of compound leaves:

Pinnate Compound

Leaves that are pinnately compound have leaflets that are attached along the petiole. Some pinnate leaves may have an odd number of leaflets with a terminal leaflet at the end of the petiole. Even pinnate leaves do not have a singular terminal leaflet and contain an even amount of leaflets.

Pinnate Compound Leaves

Bi-Pinnate Compound

Also called twice pinnate, bi-pinnate leaves have leaflets that also have leaflets. It’s like leaf inception.

bi-pinnate leaves

Palmate Compound

Palmate compound leaves typically have five or more leaflets that grow from a single point on the petiole.

Palmate Compound leaves

In Part II we will discuss leaf margins and shapes.


Parts of a Leaf
Plant Morphology
-Profant, Dennis. Trees, Shrubs, and Vines of Southeastern Ohio and Appalachia. By Bill Perine. 4th ed. N.p.: n.p., 2007. 155. Print.