Petiole

The petiole is a stalk-like structure found in the standard two-part structure of leaves. Despite looking like the stem, it is not actually a part of the stem of the plant. Additionally, the term encompasses the stalk of both simple leaves and the stalk that joins leaflets to the petiole attached at the node of a compound leaf. The petiole is not necessary to identify a leaf, but the presence of it immediately denotes the presence of a leaf.

Typically, the petiole attaches the remainder of the blade to a node on the stem. It has a variety of functions for the leaf. It acts as a channel connecting vascular tissue to the leaf, allowing for the transport of minerals and nutrients between the photosynthesizing leaf and the storage cells of the stem. Additionally, it is used in phototropism to optimize the ability of the leaf to photosynthesize by twisting it in the direction of sunlight.