petiolules

Petiolule is the small stalk that attaches a leaflet to the main axis of a compound leaf, such as the rachis or rachilla. It is the diminutive form of petiole, the stalk that supports an entire leaf. Each leaflet may be borne on its own petiolule; if a leaflet is sessile, it lacks a petiolule. The presence and length of petiolules vary among species and can be a useful feature in plant identification and description.

In compound leaves, the central axis (the rachis) bears leaflets via petiolules. The rachilla, a secondary axis in some bipinnate leaves, may also host leaflets connected by petiolules. The term helps distinguish the stalk of a leaflet from the main leaf stalk (petiole) and from other axes in the leaf’s architecture.

Etymology derives from Latin petiolus meaning “little stem,” with the diminutive suffix -ulus. In botanical descriptions, petiolule is widely used for plants with clearly stalked leaflets, particularly among many species of Fabaceae, though the term can apply to a range of taxa with compound leaves. Some authors may describe leaflets as being petiolulate or simply as having short petiolules.

Significance and variation: Petiolule length and presence can influence leaf blade orientation, light capture, and microclimate around the leaf. Variation in petiolules among related species can reflect adaptations to different environments and contribute to leaf morphology-based classification.