What is the Difference Between Stipules and Bracts

The main difference between stipules and bracts is that stipules are the leaf-like structures present on the leaf base, but bracts are the leaf-like structures present on the base of the inflorescence. Furthermore, stipules are parts of true leaves while bracts are a type of modified leaves being part of the inflorescence. 

Stipules and bracts are two types of leaf-like structures found in plants. Generally, they provide protection to the growing parts of the plants while undergoing photosynthesis. 

Key Areas Covered 

1. What are Stipules
     – Definition, Structure, Function
2. What are Bracts
     – Definition, Structure, Function
3. What are the Similarities Between Stipules and Bracts
     – Outline of Common Features
4. What is the Difference Between Stipules and Bracts
     – Comparison of Key Differences

Key Terms 

Attract Pollinators, Bracts, Inflorescence, Protection, Stipules

What are Stipules 

Stipules are the basal structures of the leaf, occurring beside the petiole in pairs. Generally, they are considered as a part of the anatomy of a typical flowering plant. However, in many plants, stipules are absent. Similarly, the size and the shape of the stipules vary with the species. Usually, they might appear as glands, scales, hairs, spines, or laminar (leaf-like) structures. Still, they commonly appear in dicots. Monocots too have stipule-like structures. 

Figure 1: Stipules

Furthermore, there are three types of stipules classified according to the duration. They are caducous, deciduous and persistent.  Typically, caducous stipules fall off before the leaf unfolds. But, the deciduous stipules fall off immediately after the leaf unfolds. However, persistent stipules remain attached to the plant.  

What are Bracts 

Bracts are the modified leaves, which occur at the base of the inflorescence. Also, they can associate with other reproductive structures of the plant, such as flowers and cone scales. Significantly, they are not different from the typical leaves at all times. However, more often, bracts are smaller, larger, or of a different color, shape, or texture in comparison to the foliage leaves. Furthermore, bracteate or bracteolate is the state of having bracts, while ebracteate or ebracteolate is the state of lacking bracts.

Figure 2: Colourful Bracts of Ananas bracteatus

Moreover, the main function of the brightly-colored bracts is to attract pollinators to the reproductive structures. For example,  Euphorbia pulcherrima (poinsettia) and Bougainvillea are common examples of flowers with large colorful bracts surrounding much smaller, less colorful flowers.  

Similarities Between Stipules and Bracts  

• Stipules and bracts are two types of modified, leaf-like structures in plants.  
• They may appear in green.  
• Their key function is to protect the growing parts of the plant. 

Difference Between Stipules and Bracts 

Definition 

Stipules refer to the basal appendages of a typical leaf of a flowering plant, usually appearing paired beside the petiole although sometimes absent or highly modified. Meanwhile, bracts refer to leaf or leaf-like structures from the axil out of which a stalk of a flower or an inflorescence arises.   

Occurrence 

Stipules occur at the base of the leaf, but bracts occur at the base of the inflorescence. 

Significance 

Stipules are the basal appendages of the leaf, but bracts are modified leaves. 

Color 

Stipules are mainly green in color, while bracts can have different colors, including green. 

Function 

The main function of stipules is to protect the next leaf, but the main function of bracts is to attract pollinators. 

Conclusion 

Stipules are the basal structures of the leaves, occurring in pairs beside the petiole. Most of the times, they appear in green color and are responsible for protecting the next leaf. In contrast, bracts are the leaf-like structures at the base of the inflorescence. However, they have different colors, sizes, and shapes. Also, they attract pollinators. Therefore, the main difference between stipules and bracts is their structure and function. 

References:

1. Hinsley, Stewart R. “6. Scales, Bracts and Stipules.” Bentham’s Outlines of Botany: Chapter 1: Section 6 – Scales, Bracts and Stipules, 2004, Available Here.

Image Courtesy:

1. “Rosa canina blatt 2005.05.26 11.50.13” By Michael Becker – taken by Michael Becker (CC BY-SA 3.0) via Commons Wikimedia   
2. “Ananas bracteatus var tricolor” By Judy Schmidt (User:Geckzilla) – Own work (CC BY-SA 3.0) via Commons Wikimedia