Birch has parallel leaf veins. Leaf arrangement (location of leaves on the stem)

Various. At the same time, they have a lot in common. Most plants have green leaves.

The leaves consist of a leaf blade and a petiole (Fig. 123).

Leaf blade

The leaf blade performs the basic functions of a leaf.

petiole

At the bottom, the leaf blade turns into a petiole - the narrowed stem-like part of the leaf. With the help of a petiole, the leaf is attached to the stem. Such leaves are called petiolate. Petiolate leaves are found in linden, birch, cherry, maple, and apple.

Aloe, cloves, flax, tradescantia, and lungwort have leaves without petioles. Such leaves are called sessile (see Fig. 123). They are attached to the stem by the base of the leaf blade.

In some plants (rye, wheat, etc.), the base of the leaf grows and covers the stem (Fig. 125). Such an overgrown base gives the stem greater strength.

Stipules

In some plants, at the base of the petioles there are stipules that look like films, scales, or small leaf-like dots (Fig. 124). The main function of stipules is to protect young developing leaves. In peas, spring cherry and many other plants, stipules remain throughout the life of the leaf and perform the function of photosynthesis. In linden, birch, and oak, filmy stipules fall off during the young leaf stage. In some plants, for example, in white acacia (Robinia pseudoacacia), the stipules are modified into spines and perform a protective function, protecting the plants from damage by animals.

The leaves of most plants range in size from 3 to 15 cm. The length of the leaves of some palm trees reaches 10 m or more. Floating, rounded leaf blades with curved edges of Victoria regia, which lives in the waters of the Amazon River, reach 2 m in diameter. Such a leaf can easily hold a 3-year-old child on its surface. And in common heather, the leaf length is measured only a few millimeters.

Simple sheet

Linden, aspen, lilac, and wheat leaves have only one leaf blade. Such leaves are called simple.

The shape of the leaf blades is varied: in aspen it is round, in lilac and linden it is heart-shaped, in wheat and barley it is linear, etc. (Fig. 126).

The leaf blades of oak and maple are divided into lobes by cutouts and are called lobed (Fig. 127). Dandelion leaves are separate, their cuts are deeper. The cutouts of the dissected leaves of yarrow and wormwood reach almost to the middle of the leaf.

Complex sheet

Rowan, chestnut, acacia, strawberry, clover, and lupine have compound leaves (Fig. 128). They have several leaf blades, which are attached to one main petiole by small petioles. During leaf fall, complex leaves do not fall off entirely: first the leaves fall off, then the petioles.

The veins are clearly visible on the underside of the leaf blades. These are conductive bundles of leaves (Fig. 129). They consist of conductive and mechanical tissues. The arrangement of vascular bundles in the leaves is called venation (Fig. 130).

Parallel venation

In iris, corn, and wheat, the veins are located parallel to one another. This is parallel, or linear, venation.

Arc venation

Kupena, lily of the valley, and plantain have arcuate venation—the veins run in arcs along the leaf.

Reticulate venation

In birch, oak, and fields, the veins on the leaves form a network. At the same time, lateral veins extend from the large central vein, which also branch. This venation is called reticulate. The reticulate veining can be finger-like or pinnate.

Palmate venation

With finger venation, several large veins extend radially from the base of the plate, like splayed fingers (maple, etc.). Material from the site

Pinnate venation

With pinnate venation, one main vein is distinguished, from which branching lateral veins extend (birch, bird cherry, oak, poplar, etc.).

The leaves on the stem are arranged in such a way as to avoid shading one another.

Next leaf arrangement

Most often, an alternate leaf arrangement is observed - the leaves on the stem are placed one after another (willow, oak, birch, cereals, blueberry, bell, apple, poplar).

Opposite leaf arrangement

With opposite leaf arrangement, the leaves are arranged in pairs, opposite each other (maple, lilac, spurge, honeysuckle, sage, mint).

Whorled leaf arrangement

If the leaves are arranged three or more per node, this is a whorled leaf arrangement (common loosestrife, bedstraw, crow's eye, oleander, elodea) (Fig. 131).

The leaves of rye, birch, sunflower, and rose hips grow one at a node and are arranged alternately on the stem in a spiral. This arrangement of leaves is called next (1).

In lilac, jasmine, maple, and nettle, leaves grow two in a node - one leaf opposite the other. This arrangement of leaves is called opposite (2).

Some plants have leaves that develop three or more at the nodes, such as elodea or crow's eye. This arrangement of leaves is called whorled (3).

SHEET

A leaf is a part of a shoot that occupies a lateral position on it.

Externally, the leaves of different plants differ greatly, but they have a lot in common. Leaves

Most plants are green in color and consist of leaf blade And petiole, with which they are connected to the stem.

If we carefully examine the leaf blade, we will see clearly defined veins on it. They contain conductive vessels through which water with minerals rises from the root, and solutions of organic substances move from the leaf to other organs. The arrangement of veins on a leaf is called venation.

In the leaves of some plants, the veins are located parallel to one another.

This type of leaf venation is called parallel. It is typical for many monocots plants (wheat, rye, barley, corn, onions).

Lily of the valley leaves have arc venation, which is also characteristic of monocots plants.

At the leaves dicotyledons Veins of plants branch repeatedly and form a continuous network. This

mesh venation.

But there are exceptions. For example, the leaves of the monocot raven's eye plant have a mesh pattern.

venation, and in the dicotyledonous plant plantain the leaf venation is arcuate.

Leaf venation: 1 – reticulate, 2 – parallel, 3 – arcuate.

If there is one leaf blade on the petiole, the leaf is called simple. Simple leaves develop from

birch, maple, poplar, oak.

A leaf consisting of several leaf blades connected to a common stalk by small

petioles are called complex. In such leaves, each blade falls off independently of the others. Compound leaves develop in ash, rowan, raspberry, strawberry, and acacia.

1, 2, 3 – simple leaves, 4, 5, 6, 7 – compound leaves.

A leaf consists of cells, cells that are not identical and perform different functions. The outer tissue covers the outside of the leaf.

Skin cells are living, they vary in size and shape. Some of them are larger, colorless, transparent and fit tightly to each other, which increases the protective properties of the skin. The transparency of the cells allows sunlight to penetrate into the leaf, where photosynthesis occurs with its help. In the picture under the number 4.

Other leaf skin cells - stomatal (1): they consist of two guard cells and, unlike other cells of the integumentary tissue, are green in color, because contain chloroplasts (3). The gap between the guard cells is called stomatal (2).

Function of stomata: transpiration – evaporation of water by leaves, as well as for the absorption of oxygen for respiration and carbon dioxide for photosynthesis (gas exchange). There are more stomata on the underside of the leaf.

Under the skin is the leaf pulp, or the main tissue. Each cell of this tissue has a thin membrane, cytoplasm, nucleus, chloroplasts, and vacuole. The presence of chloroplasts gives the green color to the tissue and the entire leaf. The cells that are adjacent to the upper skin of the leaf are elongated and arranged vertically. For the external resemblance of each individual cell to a column, the tissue is called columnar.

The main tissue lying under the columnar tissue (closer to the lower skin) is called spongy, since its cells are loosely located and large intercellular spaces filled with air are formed between them. Water vapor coming from the cells accumulates in the intercellular spaces of the main tissue.

The main leaf tissue is permeated with veins. Veins– these are conductive bundles. The veins are formed by mechanical and conductive tissues. The sugar solution formed during photosynthesis moves through the sieve tubes of the veins to all organs.

In addition to sieve tubes, the veins also include vessels through which water and minerals move from the root to the leaf cells.

Conductive bundles, in addition, also perform a supporting function - they give the sheet strength. The numerous veins include fibers. These are long cells with pointed ends and thickened lignified membranes.

The picture shows longitudinal section of the sheet: top and bottom of the sheet peel –

cover tissue, under the skin there is the main tissue (cells with chloroplasts), in the center there is a vascular-fibrous bundle. It consists of sieve tubes and vessels - conductive tissue and fibers of mechanical tissue.

FLOWER

Flowers are generative organs, i.e. involved in sexual reproduction of plants. Only as a result of flowering are fruits and seeds formed.

The most noticeable part of the flower is whisk In some plants, for example, cherry and apple trees, the corolla consists of separate petals, in others, they grow together - a long, like fragrant tobacco, or short, like a forget-me-not, tube with teeth or blades at the top is formed.

Usually the corolla is surrounded cupped, consisting of sepals. Like the corolla, the sepals can grow together or remain unfused. If the brightly colored corolla serves to attract insects, then the role of the calyx is to protect parts of the flower, especially in buds.

In the center of the flower are its main parts - stamens And pestle. The stamen consists of anther on the filament. Pollen develops inside the anther. The number of stamens in flowers varies: wheat has three thousand, cherry has up to thirty, and rosehip can have one hundred.

In the very center of the flower there is one or, less commonly, several pestles. The pestle consists of three parts: lower expanded - ovaries, medium narrow – column and top - stigma. The most important part of the pistil is the ovary, where ovules. After pollination and fertilization, seeds are formed from them, and the fruit is formed from the ovary.

1 – pistil, 2 – stamen, 3 – petal, 4 – sepal, 5 – calyx, 6 – peduncle.

The parts of a flower located around the stamens and pistil are called perianth. The perianth may consist of a calyx and a corolla, as, for example, in an apple tree, cherry tree, or poppy tree. In this case, the perianth is called double. In the tulip, lily, and iris, the perianth is not divided into a calyx and corolla, and all the leaves are homogeneous. This perianth is called simple.

All named parts of the flower - perianth, stamens and pistil - are located on receptacle – the axial part of the flower.

Most flowers develop on pedicels, which are part of the stem. But there are plants whose flowers do not have pedicels and they are called sedentary(for example, plantain).

If flowers have both stamens and pistils, they are called bisexual. Most plants have bisexual flowers.

But in some plants, for example, birch, alder, corn, cucumber, some flowers have only pistils, while others have only stamens. These are unisexual flowers. If a flower has only stamens, it is called male or staminate, and if only pestles - they call it female or pistillate.

Unisexual flowers, staminate and pistillate, can be located on the same plant, for example, birch, alder, corn, cucumber. Such plants are called monoecious. And in poplar, hemp, and willow, some plants have staminate flowers, while others have pistillate flowers. Such plants are called dioecious.

Small flowers are usually collected in inflorescences, which makes them easily visible to pollinating insects. This is the biological significance of inflorescences.

Inflorescences are groups of flowers located close to one another in a certain order.

There are inflorescences simple And complex. In a simple inflorescence, all flowers are located along the main axis, with or without pedicels (sessile).

In addition to the main axis, a complex inflorescence has lateral ones; the flowers are located only on the lateral axes.

Types of inflorescences: a – raceme, b – spike, c – spadix, d – umbrella,
d – basket, f – head, g – scutellum, h – panicle,
i - complex scutellum, k - gyrus, l - whorl

FRUIT

A fruit is a plant organ that develops from the ovary of a flower after fertilization.

What does the fruit consist of? The fruit consists of seeds and pericarp. Seed is formed from the ovule, therefore, the number of ovules in the ovary, the number of seeds formed after fertilization. Pericarp – this is the outer part of the fruit. It is formed from the walls of the ovary. But often other parts of the flower also participate in the formation of the pericarp: the receptacle, perianth, stamens, for example, in rose hips, the pericarp is formed from the receptacle.

Why does the fetus form a pericarp? The pericarp protects the seeds from drying out, mechanical damage, and adverse environmental influences. The pericarp also plays an important role in the dispersal of seeds, since some plants have thorns, prickles, produce a sticky substance, and edible fruits attract animals.

The fruits are very diverse, so they are divided into different groups. Firstly, by the number of seeds per single-seeded(wheat, sunflower) and polyspermous(pumpkin, peas, tomato).

Fruits are also distinguished by the structure of the pericarp. If the pericarp is juicy, then the fruits are called juicy, if dry, then the fruit is dry. Juicy fruits include cucumber, gooseberry, and cherry; to dry - the fruits of corn, sunflower, peas, poppy.

Sheet - This is a specialized lateral part of the shoot.

Basic and additional worksheet functions

Basic: functions of photosynthesis, gas exchange and water evaporation (transpiration).

Additional: vegetative propagation, storage of substances, protective (spines), support (antennae), nutritional (in insectivorous plants), removal of some metabolic products (with leaf fall). Leaves grow predominantly to a certain size due to regional meristems . Their growth is limited (unlike the stem and root) only to a certain size. The sizes vary, from a few millimeters to several meters (10 or more).

Lifespan varies. In annual plants, the leaves die along with other parts of the body. Perennial plants can replace foliage gradually, throughout the growing season or throughout life - evergreen plants (noble laurel, ficus, monstera, lingonberry, heather, periwinkle, cherry laurel, palm tree, etc.). The fall of leaves in unfavorable seasons is called - leaf fall . Plants that exhibit leaf loss are called deciduous (apple tree, maple, poplar, etc.).

The sheet consists of leaf blade And petiole . The leaf blade is flat. On the leaf blade you can distinguish the base, tip and edges. At the bottom of the petiole there is a thickened base leaf. Branches in the leaf blade veins – vascular-fibrous bundles. The central and lateral veins are distinguished. The petiole rotates the plate to better capture light rays. The leaf falls off along with the petiole. Leaves that have a petiole are called petiolate . Petioles can be short or long. Leaves that do not have a petiole are called sedentary (e.g. corn, wheat, foxglove). If the lower part of the leaf blade covers the stem in the form of a tube or groove, then a leaf is formed vagina (in some grasses, sedges, umbellifers). It protects the stem from damage. The shoot can penetrate right through the leaf blade - pierced leaf .

Petiole shapes

On a cross section, the petioles can have the following shape: cylindrical, ribbed, flat, winged, grooved, etc.

Some plants (rosaceae, legumes, etc.), in addition to the blade and petiole, have special outgrowths - stipules . They cover the side buds and protect them from damage. Stipules can look like small leaves, films, spines, or scales. In some cases they are very large and play an important role in photosynthesis. They can be free or attached to the petiole.

Veins connect the leaf to the stem. These are vascular-fibrous bundles. Their functions: conductive and mechanical (the veins serve as support and protect the leaves from tearing). The location and branching of the veins of the leaf blade is called venation . Venation is distinguished from one main vein, from which lateral branches diverge - reticulate, pinnate (bird cherry, etc.), fingered (Tatar maple, etc.), or with several main veins that run almost parallel to one another -– arc (plantain, lily of the valley) and parallel (wheat, rye) venation. In addition, there are many transitional types of venation.

Most dicotyledons are characterized by pinnate, palmate, reticulate venation, while monocotyledons are characterized by parallel and arcuate venation.

Leaves with straight veins are mostly entire.

Variety of leaves by external structure

According to the leaf blade:

There are simple and compound leaves.

simple leaves

Simple leaves have one leaf blade with a petiole, which can be entire or dissected. Simple leaves fall off completely during leaf fall. They are divided into leaves with a whole and dissected leaf blade. Leaves with a single leaf blade are called whole .

The shapes of the leaf blade differ in the general contour, shape of the apex and base. The outline of the leaf blade can be oval (acacia), heart-shaped (linden), needle-shaped (conifers), ovoid (pear), arrow-shaped (arrowhead), etc.

The tip (apex) of the leaf blade can be sharp, blunt, blunt, pointed, notched, tendril-shaped, etc.

The base of the leaf blade can be round, heart-shaped, sagittal, spear-shaped, wedge-shaped, unequal, etc.

The edge of the leaf blade can be entire or with grooves (not reaching the width of the blade). Based on the shape of the notches along the edge of the leaf blade, leaves are distinguished as serrated (teeth have equal sides - hazel, beech, etc.), serrate (one side of the tooth is longer than the other - pear), bearded (sharp notches, blunt bulges - sage), etc.

Compound Leaves

Complex leaves have a common petiole (rahis). Simple leaves are attached to it. Each leaf can fall off on its own. Compound leaves are divided into trifoliate, palmate and pinnate. Complex trifoliate leaves (clover) have three leaflets, which are attached to a common petiole with short petioles. Palmate compound the leaves are similar in structure to the previous ones, but the number of leaflets is more than three. Pinnately the leaves consist of leaflets located along the entire length of the rachis. There are pari-pinnate and odd-pinnate. Pairi-pinnately compound leaves (peas) consist of simple leaflets, which are arranged in pairs on the petiole. Imparipinnate leaves (rosehip, rowan) end with one unpaired leaf.

By method of division

Leaves are divided into:

1) lobed if the division of the leaf blade reaches 1/3 of its entire surface; the protruding parts are called blades ;

2) separate if the division of the leaf blade reaches 2/3 of its entire surface; the protruding parts are called shares ;

3) dissected if the degree of division reaches the central vein; the protruding parts are called segments .

Leaf arrangement

This is the arrangement of leaves in a certain order on the stem. Leaf arrangement is a hereditary trait, but during plant development it can change when adapting to lighting conditions (for example, in the lower part the leaf arrangement is opposite, in the upper part it is alternate). There are three types of leaf arrangement: spiral, or alternate, opposite and ringed.

Spiral

Inherent in most plants (apple tree, birch, rose hips, wheat). In this case, only one leaf extends from the node. The leaves are arranged on the stem in a spiral.

Opposite

In each node, two leaves sit opposite each other (lilac, maple, mint, sage, nettle, viburnum, etc.). In most cases, the leaves of two adjacent pairs extend in two mutually opposite planes, without shading each other.

Ringed

More than two leaves emerge from the node (elodea, raven's eye, oleander, etc.).

The shape, size and arrangement of leaves are adapted to lighting conditions. The relative arrangement of the leaves resembles a mosaic if you look at the plant from above in the direction of the light (for hornbeam, elm, maple, etc.). This arrangement is called sheet mosaic . At the same time, the leaves do not shade each other and use light effectively.

The outside of the leaf is covered predominantly with a single-layer, sometimes multi-layered epidermis (skin). It consists of living cells, most of which lack chlorophyll. Through them, the sun's rays easily reach the lower layers of leaf cells. In most plants, the skin secretes and creates on the outside a thin film of fatty substances - a cuticle, which almost does not allow water to pass through. On the surface of some skin cells there may be hairs and spines that protect the leaf from damage, overheating, and excessive evaporation of water. In plants that grow on land, there are stomata in the epidermis on the underside of the leaf (in wet places (cabbage) there are stomata on both sides of the leaf; in aquatic plants (water lily), whose leaves float on the surface, there are stomata on the upper side; in plants that are completely immersed in water do not have stomata). Functions of stomata: regulation of gas exchange and transpiration (evaporation of water from leaves). On average, there are 100–300 stomata per 1 square millimeter of surface. The higher the leaf is located on the stem, the more stomata per unit surface.

Between the upper and outer layers of the epidermis there are cells of the main tissue - assimilation parenchyma. In most species of angiosperms, two types of cells of this tissue are distinguished: columnar (palisade) And spongy (loose) chlorophyll-bearing parenchyma. Together they make up mesophyll leaf. Under the upper skin (sometimes above the lower one) there is a columnar parenchyma, which consists of cells of regular shape (prismatic), arranged vertically in several layers and tightly adjacent to one another. Loose parenchyma is located under the columnar and above the lower skin, consists of irregularly shaped cells that do not fit tightly to one another and have large intercellular spaces filled with air. Intercellular spaces occupy up to 25% of the leaf volume. They connect to the stomata and provide gas exchange and transpiration of the leaf. It is believed that photosynthesis processes occur more intensively in the palisade parenchyma, since its cells have more chloroplasts. In the cells of loose parenchyma there are significantly fewer chloroplasts. They actively store starch and some other nutrients.

Vascular-fibrous bundles (veins) pass through the parenchyma tissue. They consist of conductive tissue - vessels (in the smallest veins - tracheids) and sieve tubes - and mechanical tissue. The xylem is located on top of the vascular-fibrous bundle, and the phloem is located below. Organic substances formed during photosynthesis flow through sieve tubes to all plant organs. Through vessels and tracheids, water with minerals dissolved in it flows to the leaf. Mechanical tissue provides strength to the leaf blade, supporting the conductive tissue. Between the conducting system and the mesophyll is located free space or apoplast .

Leaf modifications

Leaf modifications (metamorphoses) occur when additional functions are performed.

Mustache

Allow the plant (peas, vetch) to cling to objects and secure the stem in a vertical position.

spines

Occurs in plants that grow in dry places (cactus, barberry). Robinia pseudoacacia (white acacia) has spines that are modifications of stipules.

Scales

Dry scales (buds, bulbs, rhizomes) perform a protective function - protect against damage. Fleshy scales (bulbs) store nutrients.

In insectivorous plants (sundews), the leaves are modified to trap and digest mainly insects.

Phyllodes

This is the transformation of the petiole into a leaf-shaped flat formation.

Leaf variability is caused by a combination of external and internal factors. The presence of leaves of different shapes and sizes on the same plant is called heterophily , or diversity of leaves . Observed, for example, in water yellows, arrowheads, etc.

(from Latin trans – through and spiro – I breathe). This is the removal of water vapor by the plant (water evaporation). Plants absorb a lot of water, but use only a small part of it. Water is evaporated by all parts of the plant, but especially by the leaves. Thanks to evaporation, a special microclimate arises around the plant.

Types of transpiration

There are two types of transpiration: cuticular and stomatal.

Cuticular transpiration

Cuticular Transpiration is the evaporation of water from the entire surface of a plant.

Stomatal transpiration

Stomatal transpiration- This is the evaporation of water through stomata. The most intense is the stomatal one. Stomata regulate the rate of water evaporation. The number of stomata varies among different plant species.

Transpiration contributes to the flow of new amounts of water to the root, raising water along the stem to the leaves (using suction force). Thus, the root system forms the lower water pump, and the leaves form the upper water pump.

One of the factors that determines the rate of evaporation is air humidity: the higher it is, the less evaporation (evaporation stops when the air is saturated with water vapor).

The meaning of water evaporation: it reduces the temperature of the plant and protects it from overheating, provides an upward flow of substances from the root to the above-ground part of the plant. The intensity of photosynthesis depends on the intensity of transpiration, since both of these processes are regulated by the stomatal apparatus.

This is the simultaneous shedding of leaves during a period of unfavorable conditions. The main reasons for leaf fall are changes in the length of daylight hours and a decrease in temperature. At the same time, the outflow of organic substances from the leaf to the stem and root increases. It is observed in autumn (sometimes, in dry years, in summer). Leaf fall is a plant adaptation to protect itself from excessive water loss. Together with the leaves, various harmful metabolic products that are deposited in them (for example, calcium oxalate crystals) are removed.

Preparation for leaf fall begins even before the onset of an unfavorable period. A decrease in air temperature leads to the destruction of chlorophyll. Other pigments become noticeable (carotenes, xanthophylls), so the leaves change color.

The cells of the petiole near the stem begin to rapidly divide and form across it separative a layer of parenchyma that is easily exfoliated. They become round and smooth. Large intercellular spaces appear between them, which allow the cells to easily separate. The leaf remains attached to the stem only thanks to the vascular-fibrous bundles. On the surface of the future leaf scar is formed in advance protective layer cork fabric.

Monocots and herbaceous dicotyledons do not form a separating layer. The leaf dies and gradually collapses, remaining on the stem.

Fallen leaves are decomposed by soil microorganisms, fungi, and animals.

All plants consist of vegetative and generative organs. The latter are responsible for reproduction. In angiosperms it is a flower. It is the vegetative organs of the plant - the root system and shoots. The root system consists of a main root, lateral and accessory roots. Sometimes the main root may not be expressed. Such a system is called fibrous. Shoots consist of stems, leaves and buds. Stems provide transport of substances and also support the position of the plant. The buds are responsible for the formation of new shoots and flowers. The leaf is the most important organ of the plant, as it is responsible for photosynthesis.

How it works

Consist of several types of fabrics. Let's take a closer look at them.

From a histological point of view

On top is the epidermis. This is a layer one or two cells thick with dense membranes located very close to each other. This fabric protects the leaf from mechanical damage and also prevents excessive evaporation of water from the organ. In addition, the epidermis is involved in gas exchange. For this purpose, stomata are present in the tissue.

On top of the epidermis there is also an additional protective layer, which consists of wax secreted by the cells of the integumentary tissue.

Under the epidermis layer there is columnar or assimilation parenchyma. This is a leaf. The process of photosynthesis occurs in it. Parenchyma cells are arranged vertically. They contain a large number of chloroplasts.

Under the assimilation tissue there is a conducting system of the leaf, as well as spongy parenchyma. - xylem and phloem. The first consists of vessels - dead cells, connected vertically to each other, without horizontal partitions. Through the xylem, water with substances dissolved in it enters the leaf from the root. Phloem consists of elongated living cells. Through 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.

Beneath these layers is the lower epidermis. It, like the top one, performs a protective function. It also has stomata.

Leaf structure

A petiole extends from the stem, on which the leaf blade, the main part of the leaf, is attached. Veins extend from the petiole to the edges of the leaf. In addition, at its connections with the stem there are stipules. Complex 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 like?

Depending on the structure, simple and complex leaves can be distinguished. Simple ones consist of one plate. A compound sheet is one that consists of several 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.

Leaf shape - what does it happen?

There are the following types:

• sagittal;
• oval;
• ring-shaped;
• linear;
• heart-shaped;
• fan-shaped (semicircular leaf);
• pointed;
• needle-shaped;
• wedge-shaped (triangular leaf, attached to the stem at the top);
• spear-shaped (sharp with spines);
• spatulate;
• lobed (leaf divided into several lobes);
• lanceolate (long leaf, wide in the middle);
• oblanceolate (the upper part of the leaf is wider than the lower);
• obcordate (heart-shaped leaf, attached to the stem with a sharp end);
• diamond-shaped;
• sickle-shaped.

A complex sheet can have plates of any of the listed shapes.

Plate edge shape

This is another factor that allows us to characterize a complex leaf.

Depending on the shape of the edges of the plates, leaves come in five types:

• toothed;
• crenate;
• serrated;
• notched;
• whole-edged.

Other types of compound leaves

Depending on the number of plates and their location, the following types of complex leaves are distinguished:

• palmate;
• feathery;
• bipinnate;
• trifoliate;
• finger-notching.

In palmate compound leaves, all the plates diverge radially from the petiole, resembling the fingers of a hand.

Pinnate leaves have leaf blades located along the petiole. They are divided into two types: paripirnate and imparipinnate. The former do not have an apical plate; their number is a multiple of two. In imparipinnates the apical plate is present.

In bipinnate leaves, the plates are located along the secondary petioles. These, in turn, are attached to the main thing.

Trifoliates have three blades.

The pinnate leaves are similar to pinnate leaves.

Leaves are complex - their veining

There are three types:

• go exactly from the base of the leaf to its edges along the entire plate.
• Dugovoe. The veins do not run smoothly, but in the shape of an arc.
• Mesh. It is divided into three subtypes: radial, palmate and peristonervous. With radial venation, the leaf has three main veins, from which the rest extend. Palmate is characterized by the presence of more than three main veins, which divide near the base of the petiole. In pinnately, the leaf has one main vein from which the others branch.

Most often, the complex leaf has reticulate venation.

Arrangement of leaves on the stem

Both simple and compound leaves can be arranged in different ways. There are four types of location:

• Whorled. The leaves are attached in threes to a narrow stem - a whorl. They can be cross, with each whorl relative to the previous one rotated 90 degrees. Plants with this arrangement of leaves are elodea and crow's eye.
• Rosette. All leaves are at the same height and arranged in a circle. Agave and chlorophytum have such rosettes.
• Sequential (next). Leaves are attached one to each node. Thus, they are located near birch, pelargonium, apple trees, and roses.
• Opposite. With this type of arrangement, there are two leaves on each node. 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, and jasmine.

The first two types of leaf arrangement are characteristic of plants with simple leaves. But the second two types can also refer to complex leaves.

Examples of plants

Now let's look at the different types of compound leaves with examples. There are a sufficient number of them. Plants with compound leaves come in a variety of life forms. These can be bushes and trees.

Very common plants with compound leaves are ash trees. These are trees of the olive family, class of dicotyledons, division of angiosperms. They have odd-pinnate compound leaves with seven to fifteen blades. The edge shape is jagged. The venation is reticulate. Ash leaves are used medicinally as a diuretic.

A striking example of a bush with complex leaves is the raspberry. These plants have odd-pinnate leaves with three to seven plates on long petioles. Type of venation - peristonervous. 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 rowan. Its leaves are pinnate. The number of plates is about eleven. The venation is peristonervous.

The next example is clover. It has compound trifoliate leaves. Clover has reticulate venation. The shape of the leaf edge is entire. In addition to clover, bean also has trifoliate leaves.

Plants such as Albizia also have complex leaves. It has bipinnate leaves.

Another striking example of a plant with complex leaves is acacia. This bush has reticulate venation. The edge shape is solid. Leaf type: bipinnate. The number of plates is from eleven pieces.

Another plant with compound leaves is strawberry. Leaf type: trifoliate. The venation is 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 leaves, examples, description

Type of compound sheet	Description	Examples of plants
Palmate leaves	The plates fan out from the petiole, resembling human fingers	Horse chestnut
Imparipinnate	The number of plates is odd, the apical one is present. All plates are located along the main petiole	Ash, rose, rowan, acacia
Pipirnate	The number of leaf blades is odd, the apical one is absent. All of them are located along the main petiole.	Peas, sweet peas
Bipinnate	The blades are attached to secondary petioles growing from the main petiole.	Albizia
Trifoliate (trifoliate)	They have three blades that extend from the main petiole	Clover, bean
Finger-notching	The plates are arranged like cirrus, but are not completely separated	Rowan

So we looked at the structure of a complex leaf, which ones possess them.