Stipules are small, leaf-like appendages found at the base of the petioles in many flowering plants. They are typically paired and occur in opposite positions on either side of the petiole. Stipules are considered to be modified leaves and can vary significantly in size, shape, and appearance across different plant species.
The primary function of stipules is to protect the young bud or leaf as it develops. They may also serve various other purposes, such as acting as a platform for nectar glands, providing structural support, or aiding in the regulation of gas exchange by covering tiny openings called stomata. In some cases, stipules may even play a role in defense mechanisms against herbivores or as adaptations for survival in specific environments.
The characteristics of stipules can be important for plant identification and classification. They may be determined by their shape (e.g., lanceolate, ovate, or sagittate), size (ranging from minute and inconspicuous to large and showy), texture (smooth, hairy, or spiny), color (green, reddish, or brown), and attachment points (e.g., free, connate, or adnate).
While stipules can be found in various plant families, they are particularly common in the legume family (Fabaceae). In certain species, stipules persist even after the leaf has fully expanded, while in others, they may be shed as the plant matures.
