Here we are going to discuss the parts of a leaf and leaf arrangements to help understand the lingo used to identify plants.
Let’s start with the parts of the leaf.
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 arrangements consist of leaves that are in an alternating pattern on the stem or twig.
Opposite arrangements consist of leaves that are opposite of each other on the stem or twig.
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.
Simples leaves are a singular leaf attached to the petiole.
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:
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.
Also called twice pinnate, bi-pinnate leaves have leaflets that also have leaflets. It’s like leaf inception.
Palmate compound leaves typically have five or more leaflets that grow from a single point on the petiole.
In Part II we will discuss leaf margins and shapes.