All plants consist of vegetative and generative organs. The latter are responsible for reproduction. In angiosperms, it is a flower. It is a modified escape. The vegetative organs of a plant are the root system and shoots. The root system consists of the main root, lateral and additional. Sometimes the main root may be unexpressed. Such a system is called fibrous. Shoots consist of stems, leaves and buds. The stems provide the transport of substances, and also support the position of the plant. The buds are responsible for the formation of new shoots, as well as flowers. The leaf is the most important organ of the plant, as it is responsible for photosynthesis.
How it works
Simple and compound leaves consist of several types of tissues. Let's take a closer look at them.
From a histological point of view
On top is the integumentary tissue - the epidermis. This is a layer one or two cells thick with dense shells located very close to each other. This tissue protects the sheet from mechanical damage, and also prevents excessive evaporation of water from the organ. In addition, the epidermis is involved in gas exchange. For this, stomata are present in the tissue.
On top of the epidermis there is also an additional protective layer, whichconsists of wax secreted by the cells of the integumentary tissue.
Under the layer of the epidermis is a columnar or assimilation parenchyma. This is the main fabric of the leaf. The process of photosynthesis takes place in it. Parenchyma cells are arranged vertically. They contain a large number of chloroplasts.
Under the assimilation tissue is the conducting system of the leaf, as well as spongy parenchyma. Conductive tissues are xylem and phloem. The first consists of vessels - dead cells connected vertically to each other, without horizontal partitions. The xylem carries water and dissolved substances into the leaf from the root. Phloem is made up of sieve tubes - elongated living cells. On this conductive tissue, solutions are transported, on the contrary, from the leaf to the root.
Spongy tissue is responsible for gas exchange and water evaporation.
Under the listed layers is the lower epidermis. It, like the top one, performs a protective function. It also has stomata.
Structure of leaves
The petiole departs from the stem, on which the leaf blade is attached - the main part of the leaf. Veins extend from the petiole to the leaf margins. In addition, stipules are found in its connections with the stem. Compound leaves, examples of which will be discussed below, are arranged in such a way that there are several leaf blades on one petiole.
What are the leaves
Depending on the structure, simple and complex leaves can be distinguished. Simple ones consist of one plate. A compound leaf is one that consists ofseveral plates. It can be varied in structure.
Types of compound leaves
There are several types. Factors for dividing them into types can be the number of plates, the shape of the edges of the plates, as well as the shape of the sheet. It comes in five types.
Sheet shape - what it is
There are such types of it:
- arrow-shaped;
- oval;
- ring-shaped;
- linear;
- heart-shaped;
- fan-shaped (semicircular leaf);
- pointy;
- needle;
- wedge-shaped (triangular leaf attached to the stem at the top);
- spear-shaped (sharp with spines);
- spatulate;
- bladed (the sheet is divided into several blades);
- lanceolate (long, wide leaf in the middle);
- oblanceolate (the top of the sheet is wider than the bottom);
- reverse heart-shaped (leaf in the shape of a heart, attached to the stem with a sharp end);
- diamond-shaped;
- crescent.
A complex sheet can have plates of any of the listed shapes.
Shape of plate edges
This is another factor that characterizes a complex sheet.
Depending on the shape of the edges of the plates, there are five types of leaves:
- toothed;
- crenate;
- serrated;
- notched;
- solid-edge.
Other types of compound leaves
Depending on the number of plates and theirarrangement, distinguish the following types of complex leaves:
- fingered;
- pinnate;
- two-pinned;
- three-leaf;
- perforated.
In palmate complex leaves, all plates diverge along the radius from the petiole, resembling the fingers of the hand in their appearance.
Pirate leaves have leaf blades located along the petiole. They are divided into two types: paired and unpaired. The first do not have an apical plate, their number is a multiple of two. The pinnates have an apical plate.
In bipinnate leaves, the plates are located along the secondary petioles. Those, in turn, are attached to the main one.
Three-leaved have three plates.
The pinnatifid leaves are similar to pinnate.
Leaves are compound - their venation
There are three types of it:
- Parallel. The veins run exactly from the base of the leaf to its edges along the entire plate.
- Arc. The veins do not run smoothly, but in the form of an arc.
- Mesh. It is divided into three subspecies: radial, palmate and peritoneural. With radial venation, the leaf has three main veins, from which the rest depart. The palmate is characterized by having more than three main veins that separate near the base of the petiole. With a peritoneal leaf, it has one main vein, from which the rest depart.
The most common compound leaf has reticulate venation.
Arrangement of leaves on the stem
Both simple and compound leaves canbe located differently. There are four types of location:
- Whorled. The leaves are attached in three pieces to a narrow stem - a whorl. They can be crossed, with each whorl rotated 90 degrees relative to the previous one. Plants with this arrangement of leaves are elodea, raven eye.
- Socket. All leaves are at the same height and arranged in a circle. Agave, chlorophytum has such rosettes.
- Sequential (next). Leaves are attached one at each node. Thus, they are located at the birch, pelargonium, apple tree, rose.
- Opposite. With this type of arrangement, each node has two leaves. Each node is usually rotated 90 degrees relative to the previous one. Also, the leaves can be arranged in two rows without turning the nodes. Examples of plants with this arrangement of leaves are mint, jasmine, lilac, fuchsia, lamb.
The first two types of leaf arrangement are typical for plants with simple leaves. But the second two types can also apply to complex leaves.
Examples of plants
Now let's look at different kinds of compound leaves with examples. There are enough of them. Plants with complex leaves can be of various life forms. It can be both bushes and trees.
Ash trees are very common plants with compound leaves. These are trees of the olive family, the dicotyledonous class, the angiosperm department. They have unpaired compound leaves with seven-fifteen plates. The shape of the edge is serrated. Venation - reticulate. Ash leaves are used medicinally as a diuretic.
Raspberries are a striking example of a bush with complex leaves. These plants have pinnate leaves with three to seven blades on long petioles. The type of venation is peritoneural. The shape of the leaf edge is crenate. Raspberry leaves are also used in folk medicine. They contain substances that have an anti-inflammatory effect.
Another tree with complex leaves is the mountain ash. Its leaves are paired. The number of plates is about eleven. Venation - peritoneal.
The next example is clover. It has complex trifoliate leaves. The venation of clover is reticulate. The shape of the edge of the sheet is entire. In addition to clover, bean also has trifoliate leaves.
Albizia also has complex leaves. It has bipinnate leaves.
Another striking example of a plant with complex leaves is the acacia. This bush has a mesh venation. The shape of the edge is solid. Leaf type - bipinnate. The number of plates - from eleven pieces.
Another plant with complex leaves is the strawberry. Leaf type - trifoliate. Venation - reticulate. These leaves are also used in folk medicine. Usually with atherosclerosis and other vascular diseases.
Conclusion
As a conclusion, we present a general table about complex leaves.
| Complex leaf type | Description | Examples of plants |
| Finger leaves | The plates fan out from the petiole, resembling human fingers | Horse chestnut |
| Pinnate | The number of plates is odd, there is an apical one. All plates are located along the main petiole | Ash, rose, rowan, acacia |
| Paripinnate | The number of leaf plates is odd, the apical one is missing. All of them are located along the main petiole. | Peas, sweet peas |
| Two-pinned | The plates are attached to secondary petioles growing from the main petiole. | Albizia |
| Trinity (three leaf) | They have three plates that extend from the main petiole | Clover, beaver |
| Picture cut | The plates are feathery, but not completely separated | Rowan |
So we looked at the structure of a complex leaf, its types, examples of plants that possess them.
