midrib

Midrib refers to the central vein that runs along the length of a leaf blade or leaf-like organ. It contains the primary vascular bundle, with xylem toward the upper side and phloem toward the lower side, and is often reinforced by supportive tissue. The midrib connects the blade to the stem via the petiole and acts as the main conduit for water, minerals, and photosynthates between the stem and leaf tissues. It also provides mechanical support to help keep the blade upright and resistant to bending.

In simple leaves, the midrib is the prominent central vein from base to tip. In leaves with compound structure, the central axis is the rachis, and each leaflet may have its own midrib or axial veins; some compound leaves do not have a single, obvious midrib across the entire blade. Leaves with reticulate venation, common in dicots, typically show the midrib with a network of secondary veins branching from it, while many monocots exhibit parallel venation where longitudinal veins run roughly side by side.

The prominence and thickness of the midrib vary among species and leaf types and can reflect functional and ecological adaptations, including light capture efficiency and mechanical resilience. The term is widely used in leaf anatomy and plant identification to describe the leaf’s central vascular channel and its role in the leaf’s overall vascular and structural system.