'' with phyllode between the branch and the
compound leaves at both ends of the petioles of
Elaeocarpus multiflorus The petiole is a stalk that attaches a leaf to the rest of a plant. In some species, it is able to twist the leaf to face the sun, thus optimizing its exposure to sunlight. In some other plant groups, such as the speedwell genus
Veronica, petiolate and sessile leaves may occur in different species. 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. In some plants, the petioles are flattened and widened to become
phyllodes (also known as phyllodia or cladophylls) and the true leaves may be reduced or absent. Thus, the phyllode comes to serve the functions of the leaf. Phyllodes are common in the genus
Acacia, especially the Australian species, at one time put in
Acacia subgenus
Phyllodineae. In
Acacia koa, the phyllodes are leathery and thick, allowing the tree to survive stressful environments. The petiole allows partially submerged
hydrophytes to have leaves floating at different depths, the petiole being between the node and the stem. ==Etymology==