Leaves are the most important parts of most plants. Thanks to them, there is a movement of water through the plant mass, the transformation of sunlight into growth energy and purification of the air. There are many biological classifications of leaves based on various signs. In the framework of this article, we will consider the main of them.
What is a sheet?
A sheet is an outer part of the plant, which is responsible for photosynthesis, evaporation of water and gas exchange between the plant and the environment. The vast majority of plants have them, from barely noticeable grass to huge trees. With the word “sheet”, the imagination immediately draws a classic leaf, like a birch. However, there are a huge number of variations of forms and structures, any of which serves for the same purposes.
The main types of leaves
The simplest classification of plant leaves is carried out according to their form. According to her, there are leafshaped processes (for example, in fern), flowering plant leaves (classic shape with a petiole and leaf plate), needles and lamp leaves (common in herbs).
Species determined by the location on the stem
Another or sequential location means that the leaves begin to grow on a stem for one node. The term “knot” indicates a place on the stem, which is used for the formation of a new sheet.
Supply arrangement means that two leaves grow on each node of the branch or stem. Moreover, in many cases, each subsequent node rotate 90 degrees relative to the previous.
The outlet placement of leaves implies their location at the same height and orientation in a circle. Roughly speaking, all sheets of such a plant grow from one point (root) and form a beautiful sprawling bush.
There is also a mutual location. It is similar to a opposite, but has three sheets on the knot. In this case, the nodes are called mutovs and can also be sequentially deployed by 90 degrees.
Classification by type of sheet plates
This classification is based on the number and separation of leaflets growing on one cuttings, or from one node of the stem (barrel). In accordance with this, the easiest type is a simple sheet. It is characterized by the presence of only one sheet plate and one petiole. The plate is called the surface of the sheet, that is, its “canvas” with the veins. In a simple sheet, it can have any shape, but cutouts never reach the petiole. The leaves of a simple type always fall along with the petiole, leaving not a single part on the tree.
The next type is a complex sheet. Here several leaves are attached to one petiole at once. Moreover, each of them can have its own additional petiole.
Types of leaves by their form
The classification in the shape of the sheet is very extensive. After all, there are a huge number of plants with a wide variety of foliage. This list includes more than 30 names, each of which describes a certain form. We will not list them all, we will only say about the most common.
Perhaps the most familiar type of this classification is thyroid. Leaves of this shape have, for example, birch. They look like a small shield and at the same time have classic outlines of the sheet. There are unusual ones, like a “nalesheartshaped”. This type has the shape of an elongated heart, the lower, sharp end adjacent to the petiole.
Also interesting are mutated leaves. This type is usually found in various field herbs and many colors. The type of “peristrostan” is familiar to everyone since childhood the leaves of this form have a dandelion.
Nonstandard evolution of leaves
During the evolution of the foliage of trees and plants, she underwent various changes. In most representatives of the flora, they did not lead to serious changes, but the leaves of certain plants began to perform specific functions.
Perhaps the most “highly specialized” are the hunting leaves. They are present on predatory plants that feed on insects. A striking example Rosyanka or Venus Mukholovka. The main task of such a sheet is to catch an insect, to ensure its retention, and to digest using special enzymes. The method of capture is different: in some cases, the sheet produces sticky juice (mowing), in others it is sharply closed (Venus flyer), and special bubbles with valves (bubbles) come into effect in the third.
This type of leaves is designed to create water reserves. The most familiar plant with them is aloe. Thick and fleshy, they contain a large amount of moisture inside, since such flowers grow in arid regions with a small amount of precipitation.
This type also stores water, but does this not at the expense of a thick layer of pulp, but with a funnel. The funnel is formed by the sheet itself, which is twisted in a special way and holds the accumulated rain water.
In order to protect, the leaves of some plants were evolved into thorns. They can be a modified leaf plate, hardened and pointed, and can form from shoots.
Leaves-asses are available on creeping plants that need support. Are a continuation of the upper parts of ordinary leaves in the form of long, curly processes. They cling to the surrounding objects, so the plant wraps them out. This type of leaves has ordinary garden peas, cucumber, pumpkin.
Fillodiya is a special case of the evolution of the petiole. Such a petiole is similar in shape to a sheet and is able to perform photosynthesis. In this case, a real sheet located further has a simplified structure and degrades.
This type of leaves is characterized by their semicircular or circular shape, often with the formation of a small funnel. In the formed deepening, as a rule, leaves of a different type or inflorescence are located.