A plant stipule is a small, leaf-like appendage located at the base of the petiole (leaf stalk) where it attaches to the stem. They are typically paired, occurring on either side of the petiole.
Details about Stipules
Stipules are considered part of a flowering plant's normal anatomy, though their form and function can vary greatly. They may appear as:
- Leaf-like structures: Resembling small leaves.
- Spines: Offering protection.
- Glands: Secreting substances.
- Scales: Protective coverings.
- Tendrils: Assisting with climbing.
- Reduced or absent: In some species, they are inconspicuous or entirely absent.
Function of Stipules
The primary function of stipules is often to protect the developing leaf bud. However, they can also contribute to:
- Photosynthesis: When leaf-like.
- Defense: When modified into spines or glands that secrete defensive compounds.
- Support: When modified into tendrils.
Examples of Stipules
- Pea plants: Have stipules that are often larger than the leaflets.
- Roses: Often have stipules that are fused to the petiole.
- Acacias: Sometimes have stipules modified into spines.
Types of Stipules
While there isn't a strict classification, stipules can be broadly categorized based on their appearance and attachment:
- Free Stipules: Separate from the petiole.
- Adnate Stipules: Fused to the petiole for at least part of its length.
- Ochreate Stipules: Forming a sheath around the stem (characteristic of the Polygonaceae family).
In conclusion, stipules are foliar appendages found at the base of the leaf petiole, exhibiting a wide range of forms and functions, primarily related to protection and sometimes contributing to photosynthesis, defense, or support.
