Petiolule

In botany, the petiole (/ˈpiːtᵻoʊl/) is the stalk that attaches the leaf blade to the stem. The petiole is the transition between the stem and the leaf blade. Outgrowths appearing on each side of the petiole in some species are called stipules. Leaves lacking a petiole are called sessile or epetiolate.

The petiole is a stalk that attaches a leaf to the plant stem. In petiolate leaves, the leaf stalk (petiole) may be long, as in the leaves of celery and rhubarb, short or completely absent, in which case the blade attaches directly to the stem and is said to be sessile. Subpetiolate leaves are nearly petiolate, or have an extremely short petiole, and may appear sessile. The broomrape family Orobanchaceae is an example of a family in which the leaves are always sessile. In some other plant groups, such as the speedwell genus Veronica, petiolate and sessile leaves may occur in different species.

In the grasses (Poaceae) the leaves are apetiolate, but the leaf blade may be narrowed at the junction with the leaf sheath to form a pseudopetiole, as in Pseudosasa japonica.

In plants with compound leaves, the leaflets are attached to a continuation of the petiole called the rachis. Each leaflet may be attached to the rachis by a short stalk called the petiolule. There may be swollen regions at either end of the petiole known as pulvina (singular=pulvinus) that are composed of a flexible tissue that allows leaf movement. Pulvina are common in the bean family Fabaceae and the prayer plant family Marantaceae. A pulvinus on a petiolule is called a pulvinulus.

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