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 palmate 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).
Linden (Tilia) is a deciduous tree, including up to 45 species. It grows mainly in the temperate zone of the Northern Hemisphere. There are 7 wild species and 10 hybrids common in Russia. Small-leaved and heart-shaped linden are more common. In Ukraine and Moldova, mainly European, large-leaved, felt, and Hungarian linden grows. In the Caucasus and Crimea - Crimean, Caucasian, pubescent columnar. In the Far East, Amur, Korean, Chinese, spreading, and Manchurian linden are common. In Tatarstan, Mordovia and Chuvashia, pure linden groves (lime forests) have been formed. The maximum age of linden forests is 400 years. In single plantings, the tree can live up to 1200 years. On city streets, the age of this plant is reduced to 100 years. Linden is a companion of oak, maple, ash, spruce and pine. The placement of the plant is uneven and depends on natural conditions and human activity. Under natural conditions, it reproduces by stump shoots.
The habitats of this plant can be forest lands and city streets. Artificially created linden plantations are found along roads, in parks, squares, gardens, around fields, apiaries, and ponds.
The most popular is the small-leaved linden, used in medicine and the national economy. A species very close to it grows in Western Siberia - the Siberian linden.
The linden tree is a source of a pleasant, strong aroma, as well as an effective remedy in the fight against colds.
Trunk, bark and stem of linden
In forest stands, trees have a straight trunk, highly cleared of branches, and a highly raised, thin crown. In open plantings the crown is denser and located lower. The lower branches of the linden tree extend from the trunk and rise, the middle branches extend horizontally from the trunk, and the upper ones rise upward at an angle. The foliage of the tree is dark green, with drooping yellow-white flowers - semi-umbels and yellow-green bracts. The crown shape is tent-shaped. Complete crown formation ends at the age of 40 years.
The bark of young linden is smooth, light gray; in adults it is thick, dark gray, covered with deep grooves and cracks.
The linden stem has a structure typical of all trees. In its center there are thin-walled core cells where nutrients accumulate. The core is surrounded by a thick layer of wood, which makes up 90% of the total volume of the stem.
This plant is a diffuse-vascular, mature woody, kernel-free species. It has soft wood of a white, pink, or reddish hue. It has a blurred, inexpressive texture, so the annual layers on sections can be traced rather poorly. On a transverse section, narrow heart-shaped rays in the form of thin lines are visible; on a radial section, dull stripes and blurry dark spots can be seen. Late wood is no different in density from early wood. There are 4.5 annual layers per 1 cm cross section. The vessels are thin and invisible. The structure of the wood is homogeneous. Humidity is distributed evenly over the cross section of the trunk.
Leaf arrangement and linden leaf
The linden leaf is simple, heart-shaped, pointed, the edges are finely toothed, with large veins, dark green above, light green below, with reddish hairs. It is supported by a reddish petiole 1-3 cm long.
It contains calcium, so when it falls it quickly decomposes, thereby improving the properties of the soil and increasing its fertility.
Over 1 year, the mass of dry linden leaves during decomposition decreases by 70% of the original mass.
Moreover, intensive decomposition occurs in the spring-summer period, which is most favorable for the development of microorganisms in the soil. Freshly fallen leaves contain ash, potassium, calcium, nitrogen, and sulfur.
Linden buds and root
Linden buds are reddish-brown, smooth, covered with scales, ovoid in shape, arranged in two rows. Length 6-7 mm, width 3-5 mm. Each bud contains 5 leaves with stipules and two rudimentary leaves. The shoots are brown-brown, covered with lentils.
The root system of the plant on fertile, fresh, loose soils is powerful, highly developed, has a tiered structure, and uses nutrients from all layers of the soil. The linden root goes deep into the ground and gives off well-developed lateral roots. Linden also has a superficial root system formed by adventitious roots.
The flowers are bisexual, small, regular in shape, collected in racemes (umbrellas), have 5 sepals, a corolla with 5 petals, a pistil and several stamens. Flowering begins in June and lasts until mid-July. Flowering duration is up to 14 days. The tree begins to bloom at 20-25 years of age.
Flowering and nectar production depend on the plant’s habitat, geographic, environmental and other factors. However, it has been noticed that the linden begins to bloom when the bees have the maximum opportunity to use nectar. Nectar in linden flowers is secreted by nectar-bearing tissue and is retained inside the sepals. The released nectar is not reabsorbed.
Linden branch and seeds
The period of tree maturation begins at the age of 20-30 years. The linden branch becomes strong enough to ensure flowering and seed ripening.
At this age, a large number of inflorescences appear. Linden seeds ripen in autumn.
Spread by wind, animals and birds. They are especially noticeable on snow crust. They are collected from October to March.
The fruit is a spherical, elongated nut containing 1, 2, rarely 3 seeds. The fruit shell is dense and waterproof.
Features of linden
The plant is quite shade tolerant. On this basis it is second only to coniferous species, beech and oak. A shade-tolerant linden tree with a wide spreading crown often shades the soil for other plants. Frost-resistant. Among broad-leaved trees, it penetrates farthest to the north, growing in harsh conditions at very low temperatures. It is not afraid of frost, as it blooms late. Resistance to frost is explained by the short period of shoot growth, the high ability to retain water in the leaves, as well as the high oil content in the branches. Linden fats contain unsaturated linolenic acid, which quickly oxidizes and generates heat, so in winter linden can withstand temperatures down to -50°C.
Sometimes frost cracks form on the south side of the trunk and branches of the tree. This is due to the sharp temperature change. In harsh winters with little snow, young shoots and roots can freeze. In some cases, the cause of death of young individuals may be the lack of insulation with a layer of snow. Strong winds also negatively affect the development of the plant. The tree is drought-resistant, but if there is excessive drought, growth decreases. The mosaic arrangement of linden leaves protects from strong sun and dry climate, when the outer row forms a solid green ball, shading the area with the root system.
Linden does not like excessive soil moisture, waterlogging and flooding. Tolerates air pollution and is smoke resistant. On fertile soils, its gas resistance increases. The small-leaved linden is considered the most unpretentious species of this plant. It can grow in different soils, except swampy, excessively salty and dry. Prefers loose, humus-rich areas.
Linden trees growing in the zone of podzolic soils indicate high soil fertility in this area. In the forest-steppe zone, the presence of linden indicates leaching of the soil. The growth of the tree in the undergrowth of pine forests indicates highly productive conditions. This is due to the fact that the litter formed from leaves, pine needles, fallen branches and bark forms neutral humus containing ash elements that reduce the acidity of the soil and increase the degree of its saturation.
After cutting down a tree, stump growth forms. It appears around the neck of the root and begins to germinate profusely. The property of linden is to produce dense growth and continues until old age. At age 100, this ability begins to decline. After clear cutting, linden shoots begin to densely populate the cutting area, suppressing self-seeding and slowing down the growth of conifers.
Linden tolerates pruning well, so its crown can be given any shape. This tree is often used to create parks, squares and alleys.
Leaf arrangement e - the order of placement of leaves on the shoot axis (Fig. 26). May be:
Leaf classification
There are simple and compound leaves. Leaves that have one blade (whole or notched) are called simple. Simple leaves withl
Rice. 27. Compound Leaves: 1 - trifoliate; 2 - finger-compound; 3 - odd-pinnate; 4 - pari-pinnate.
Compound Leaves- - leaves consisting of several clearly separated leaf blades (leaflets), each of which is attached with its petiole to a common petiole (rachis). Often a complex leaf falls off in parts: first the leaves, and then the petiole.
Depending on the location of the leaflets, they are distinguished (Fig. 27):
Pinnately leaves - leaves in which the leaflets are located on the sides of the rachis. When the apex of the rachis ends in one unpaired leaf, such leaves are called odd-pinnate(rose hips, white acacia). U paripirnate leaves, all leaves have a pair (peas, yellow acacia).
Palmate compound leaves - leaves in which the leaflets are not located along the length of the rachis, but only at its top in one plane (chestnut, lupine).
A special case of a complex worksheet is trifoliate leaf - a leaf with only three leaves (clover, oxalis).
The rachis of compound leaves can form lateral branches, then double-, triple-, quadruple-pinnate leaves appear. For example, mimosa has a double-pinnate leaf.
Leaf venation
Venation is a system of conducting bundles in leaf blades.
Rice. 28. Leaf venation:
1 - parallel; 2 - arc; 3 - mesh with a pinnate arrangement of the main veins; 4 - mesh with a finger-like arrangement of the main veins; 5 - dichotomous.
The nature of the arrangement of the veins and the shape of the leaf blades are closely interrelated (Fig. 28). There are:
simple venation- only one vein penetrates the leaf blade from the base to the apex (mosses, mosses);
dichotomous venation- the leaf blade is pierced by forked veins (ginkgo);
arc venation- the leaf blade from the base to the apex is pierced by several identical veins, arranged in an arched manner (lily of the valley, hellebore);
parallel venation- the leaf blade from base to apex is pierced by several identical veins arranged strictly parallel (rye, sedge);
reticulate venation- usually one vein enters the leaf blade from the petiole, which then gives off branches - lateral veins, forming a dense network. Reticulate venation can be pinnate or palmate.
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.), serrated (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 yellow, arrowhead, 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 promotes 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.
The shape of the leaves of different plants is not similar to each other. But even the most diverse leaves can always be combined into two large groups. One group consists of simple leaves, the other - complex leaves.
How to distinguish a simple sheet from a complex one? There is only one leaf blade on the petiole of each simple leaf. And compound leaves have several leaf blades located on one petiole, which are called leaflets.
Among simple leaves, there are whole, lobed, divided and dissected leaves.
Many trees have whole leaves: birch, linden, poplar, apple, pear, cherry, bird cherry, aspen and others. A leaf is considered whole if its blade is entire or has shallow notches.
Bladed they call a leaf in which, like an oak, the cut-out blades along the edges of the blade reach one quarter of its width.
If the cuts in the leaf blade do not reach the midrib or base of the leaf slightly, the leaves are called divided. If the leaf is cut to the midrib or to the base, it is called dissected.
Lobed leaves- these are the leaves of maple, oak, hawthorn, currant, gooseberry and some other plants.
Take several leaves of different plants, for example: raspberry, rowan, ash, poplar, maple, oak. Compare the leaves of rowan, raspberry, and ash with the leaves of poplar, linden, maple and oak. How are they different from each other? The leaves of ash, rowan and raspberry have several leaf blades - leaflets - on one petiole. These are compound leaves. The leaves of poplar, maple and oak are simple. In simple leaves, the leaf blade falls off along with the petiole during leaf fall, while in complex leaves, the individual leaves that make up the leaf may fall off earlier than the petiole.
A compound leaf consisting of three leaf blades, like a clover, is called trisyllabic or trifoliate.
If a leaf is formed by several leaf blades attached at one point, as, for example, in lupine, it is called palmate compound. If the leaves of a compound leaf are attached along the entire length of the petiole, then such a leaf is pinnately complex.
Among pinnately compound leaves, a distinction is made between imparipinnate and paripirnate.
Imparipinnate leaves are those that end in a leaf blade that does not have its own pair. An example of imparipinnate leaves would be the leaves of rowan, ash, and raspberry. Piripnately compound leaves are less common, but you still know some plants with such leaves. These are, for example, field peas, mouse peas and sweet peas.
Both simple and compound leaves of dicotyledonous and monocotyledonous plants are arranged on the stems in a certain order. The portions of the stem that bear leaves are called stem nodes, and the sections of the stem between the nodes are called internodes.
The arrangement of leaves on the stem is called leaf arrangement.
Most plants have alternate leaf arrangement, for example: rye, wheat, birch, apple tree, sunflower, ficus, rose. Their leaves are arranged spirally around the stem one at a time, as if alternating with each other, which is why this arrangement is called alternate.
The leaves of lilac, jasmine, maple, fuchsia, and dead nettle are located on the stem not one at a time, but two at a time: one leaf opposite the other. This leaf arrangement is called opposite.
Sometimes there are plants with whorled leaves. Their leaves grow on the stem in bunches, whorls, arranged in three or more leaves per node, and form a kind of ring (whorl) around the stem. Among indoor plants, oleander has a whorled leaf arrangement, in an aquarium - elodea, among wild plants - northern bedstraw, lupine clover, four-leaf raven's eye and other herbaceous plants.