Petiole: Definition & Function

Petiole: Definition & Function
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  • 0:00 Definition of a Petiole
  • 0:20 Simple Leaves: Structure
  • 0:59 Compound Leaves: Structure
  • 1:35 Petiole Function
  • 2:25 Examples
  • 3:35 Lesson Summary
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Lesson Transcript
Instructor: Thomas Higginbotham

Tom has taught math / science at secondary & post-secondary, and a K-12 school administrator. He has a B.S. in Biology and a PhD in Curriculum & Instruction.

In some plants, the petiole is the part of the plant that connects the leaf to the stem of the plant. In this lesson, learn what a petiole is, and is not, while becoming familiar with some petiole plants and trees.

Definition of a Petiole

If you've eaten a celery stalk, you've eaten a petiole, the part of some plants that connects the blade of a leaf to its stem. In terms of their function, petioles play an important part in photosynthesis. They are also responsible for the dramatic way deciduous trees lose their leaves in the fall.

Simple Leaves: Structure

Let's took a deeper look at petioles and their role in plant life. Before getting into petioles, it is important to understand what a leaf is and the different types of leaves. Leaves are the green part of flowering plants that are generally flat; this is where photosynthesis and transpiration occur. Leaves originate and attach to the stem of a plant from a bud, the flat area of a leaf that most people think of as 'the leaf' is actually called the blade or lamina of the leaf.

In a sessile leaf, the blade of a leaf connects directly to the stem and has no petiole. In a petiolate leaf, the blade of the leaf has a petiole, also known as a leaf stalk.

Compound Leaves: Structure

Simple leaves have only one main blade that originates from the bud. When a leaf has multiple blades originating from a single bud, it is called a compound leaf, and the individual blades within the single leaf are called leaflets.

'Compound leaves (that are petiolate) are still connected to the plant stem by a petiole. However, the petiole ends where the blades begin. Thereafter, moving out towards the tip of the leaf, the main axis of the leaf is called the rachis. Individual leaflets are connected to the rachis not by petioles but by petiolules. Finally, the entire structure from the leaf bud to the terminal leaflet is considered a single leaf.

Petiole Function

The petiole is the pipeline through which the products of photosynthesis are moved from individual leaves to the rest of a plant. During this process, necessary chemicals and nutrients from other parts of the plant (such as nutrients absorbed through the roots) are transported to individual leaves.

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