stipula

Stipula, in botanical terminology, refers to a stipule (singular) or stipulae (plural): a small outgrowth located at the base of a leaf stalk (the petiole) in many flowering plants. In most species, a pair of stipules sits at the base of each leaf, one on each side of the stem, though their position can vary. Stipules may be leaf-like (foliaceous), scale-like, or hair-like, and in some plants they are fused around the stem or between leaf bases to form a protective ring or sheath.

Stipules exhibit considerable morphological diversity. They can be free or adnate to the petiole, persistent or deciduous, and they may be simple or subdivided. In some lineages, stipules are greatly enlarged and modified into structures such as spines, glands, or tendrils, while in many grasses and related monocots stipules are reduced or absent, with other structures like ligules taking their place.

The function of stipules varies by group. Traditionally they are thought to protect young growth during leaf development, particularly in early stages when the bud is vulnerable. In species with foliaceous stipules, the stipules can contribute to photosynthesis or leaf area; in others, their role is mainly protective or structural. Developmentally, stipules arise from the leaf axil and often share vascular connections with the leaf.

Stipules are valuable in plant identification and taxonomy, providing diagnostic characters for many families and genera. The term stipula is typically used to describe the singular element in botanical descriptions.