Leaf arrangement, or phyllotaxis, is a certain scheme by which leaves are located on the stem of a plant. Even at first glance it can be determined that they never grow in a chaotic manner, and there are important reasons for this.
Light access
Why, then, leaves do not grow there, "wherever they like"? The reason, of course, is lighting. As a result of evolution, several types of leaf arrangement were formed that provide each sheet with maximum light access. So, the leaves of the same plant do not compete with each other. As a rule, the pattern of leaf placement is associated with the shoot apex, reflecting its symmetry along the radius. When describing the leaf location in morphology, they usually rely on the number of leaves that extend from one node.
Schemes
Leaves can be arranged in three main patterns, which are called so: regular, whorled and opposite. It’s easy to remember: next time - one sheet from one node, when opposite - two sheets, and when whorled - three or more (for example, an elodea has more than three leaves). The latter is one of the most common types of location characteristic of herbaceous plants. The leaves grow from one node, forming around the stem a so-called whorl - a ring. This pattern is characteristic of herbaceous plants, for example, northern bedstraw, lupine clover and four-leafed crow's eye.
In a separate type of phyllotaxis, you can include a socket that should not be confused with whorled. A rosette is formed by leaves with different leaf positions, if the stem is shortened. This can be observed in plants such as agave, chlorophytum, saxifrage, and others.
In a row
The next leaf location, or, as it is also called, spiral, involves the growth of leaves, one for each node. To understand and remember this species, just look at the branch of oak or birch. The leaves are arranged on the stem alternately in a spiral.
As a rule, in lower forms the arrangement of leaves is opposite, and in more advanced plants it is another.
Heredity
In adult shoots, the leaf location, the next one or another type, is determined by the order of origin of the leaf primordium. These are leafy buds of plants. It happens that some type of phyllotaxis is characteristic of all plants of the same family. However, the leaf position may change during shoot growth. Petioles can also bend in various ways, so the leaf blades can also change their position. This is due to the fact that the leaves are constantly in search of the best position, where they will receive the maximum amount of light.
In the end, the distance between large leaves is filled with smaller ones, not shading each other, forming a continuous sheet cover. The phenomenon was called "sheet mosaic." It allows the plant to make maximum use of all the sunlight that can fall on the leaves. This feature is characteristic of all types of phyllotaxis, and another leaf arrangement is no exception. Examples will be given below.
Examples and properties
The next leaf arrangement on our planet has many plants. Almost all deciduous tree species that grow in Central Russia have another phyllotaxis, and not only the leaves, but also the branches are located this way. These are oaks, birch, aspen, among garden trees - plums, apple trees and cherries, and shrubs - currants, gooseberries, black chokeberries.
Interestingly, there are two exceptions to this list. Ash property - has the opposite arrangement. Holly maple, popularly called Canadian, has the same phyllotaxis, but the American maple (ash) has another leaf arrangement.