November 28, 2021
The petiole (English: petiole, leaf stalk) is a small stalk that connects the leaf blade and the stem in a plant, and is one of the organs that make up the leaf. The leaves basically consist of three organs: leaf blade, petiole, and leaf stalk. The petiole supports the leaf blade and functions as a passage for water, nutrients, and anabolic substances to move between the stem and the leaf blade. .. The petioles often have leaves, but they are well-developed in the leaves of dicotyledonous plants, and are said to be present in 40% of woody plants and 20% of herbaceous species.
There are also species such as legumes that cause orientation movements to direct the leaf blades toward sunlight, or change the direction of the leaf blades by making small changes in the length of the petiole.
In compound leaves, the central axis of the leaf to which the leaflet is attached is called the leaf axis (yojiku, rachis, rhachis), and the petiole pattern in the compound leaf is called the petiole.
The petioles come in a variety of shapes, including those with a circular cross section, those with a semicircular cross section, and those with a groove on the opposite axis side. In Nandina domestica Thunb. And Umbelliferae, the base of the petiole enlarges to form a pod and protects the axillary buds. The shape of the vascular bundle inside the petiole shows various types depending on the taxon, and as a whole, collenchyma and sclerenchyma develop.
The linear leaves of monocotyledons (ensiform leaves) are said to originate from petioles (see the false leaf theory below). Also, in monocotyledons (and some of the eudicots), the lower part of the leaf embraces the stem, often forming a leaf sheath, which is also the part where the petiole is enlarged. It is also said that the petiole and dicotyledon are fused.
Petioles are not found on all leaves, but leaves with petioles such as Betula platyphylla Sukaczev are petiolate leaves, and petioles such as Gentiana zollingeri Fawc. And Zinnia elegans Jacq. A leaf with no petiole and a leaf blade directly connected to the stem is called a sessile leaf. The absence of petioles is called muhei.
It is sessile in gymnosperms except Ginkgo biloba L. and Gnetum, and at least the stem leaves are sessile in Dianthus L., St. John's whale, Hypericum L., Gentianaceae, and Anaphalis DC.
As in the case of Brassica rapa L. var. Oleifera DC. It is called amplexicaul leaf. Having a stalk leaf is called amplexifoliate. Among the sessile leaves, the leaf legs of one leaf, such as Tricyrtis perfoliata Masam. The leaves where the bases of two opposite leaves are united with each other and the leaf blades can be seen penetrating the stem are called honeysuckle leaves (perfoliate (d) leaf) or honeysuckle leaves. In the long branches of Lonicera gracilipes Miq., The base of the petiole is stalked and becomes disk-shaped. Furthermore, the flow of the base of the petiole along the stem in a wing-like manner is called along (enka-or along, decurrent).
They vary in length, and short petioles such as Quercus serrata Murray are called short petioles, and long petioles such as Smooth Pigweed Amaranthus hybridus L. are called long petioles. In the genus Chickweed Stellaria L., the length may differ between one branch, and in the floating leaves, the genus Marsilea L. and the genus Nuphar Sm., The length varies depending on the water depth.