midvein

The midvein, also called the midrib, is the main central vascular bundle of a leaf, extending from the base of the blade near the petiole to the tip. It acts as the primary axis along which the leaf blade is organized and provides structural support to keep the leaf upright and resistant to bending.

Anatomically, the midvein consists of vascular tissues, typically arranged as xylem and phloem within a collateral or similar bundle. It is often reinforced by supportive sclerenchyma tissue and is embedded within the leaf’s mesophyll and epidermis. The exact arrangement can vary among species, but the midvein generally serves as the main conduit for transporting water, minerals, and photosynthates between the stem and the leaf.

Functionally, the midvein performs two key roles. It conducts water and dissolved minerals from the stem into the leaf machinery, and it distributes synthesized sugars from the leaf to other parts of the plant. It also provides mechanical strength, helping the leaf maintain its shape and resist environmental forces such as wind and gravity.

In the broader context of leaf venation, the midvein is the central axis in leaves with pinnate venation, from which lateral veins branch toward the margins. In leaves with parallel venation, common in many monocots, a prominent central vein may serve a similar structural role, though the pattern differs. The visibility and thickness of the midvein vary among species, leaf ages, and environmental conditions, and the term is sometimes used interchangeably with midrib.

See also: leaf venation, vascular tissue.