Leaves are the most sensitive organs of plants to the environment, and their morphological structure is most likely to change with different ecological conditions to adapt to the environment.The leaves of different plants have various shapes, sizes and shapes.But as for a plant, it is relatively stable and can be used as a basis for plant identification and classification.At the same time, the leaf color is also diverse. Generally speaking, the chlorophyll andCaroteneThe molecular proportion of is about 3:1, which makes the leaves green.[1]
On the cross section, the leaf structure consists of epidermis, mesophyll and vein.[1]
Chinese name
leaf
Foreign name
Leaf
Features
Photosynthesis to synthesize organics
Role
Photosynthesis, transpiration, absorption and secretion, reproduction, etc
The leaves are generally composed ofpetioleandStipuleThree parts, such as the leaves of cotton, peach and pea, are called complete leaves.The leaves lacking any part or two of them are calledIncomplete leaf, such as sweet potato, rape, sunflower and other leaves lack stipules;Leaves of tobacco and lettuce lack petioles and stipules;Some plants even have no leaves, but only a flattened petiole, called leaflike petiole, grows on the stem, such asTaiwan AcaciaEtc.[2]
GramineaeThe leaves of plants are different from those of ordinary plants. They are composed of leaves and leaf sheaths.The leaf blade is linear or strip shaped, which is a longitudinal parallel venation.The leaf sheath is long and narrow, holding the stem, and has the functions of protection, support and conduction.[3]
blade
The leaf is the most important part of the leaf, mostly a thin green flat body. This thin and flat shape has a large surface area, which can shorten the distance between the mesophyll cells and the leaf surface, and the leaf veins that play a supporting and conducting role are also in a network state.These characteristics are conducive to gas exchange and light energy absorption, as well as the input of water and nutrients and the output of photosynthetic products. They are perfect adaptations to photosynthesis and transpiration.[4]
Leaf veins of different sizes are distributed in the leaves. One of the most obvious veins along the central longitudinal axis of the leaves is called the main vein, and the other veins are called lateral veins.The dicotyledonous plants send out many lateral veins from the main vein to both sides, and the lateral veins divide into veinlets. The lateral veins and veinlets cross each other to form a network, called reticulate veins;The main veins of monocotyledonous plants are obvious, and the lateral veins are sent from the base to the tip of the leaf. The veins are parallel, which is called parallel veins.The leaf veins of some lower angiosperms, ferns and gymnosperms are bifurcated to form forked veins, which are relatively primitive leaf veins.[4]
The leaf can also be divided into leaf tip, leaf base, leaf edge and other parts. The morphological characteristics of each plant leaf can be used as one of the basis for identifying plants.[4]
petiole
The petiole is a petiolate part next to the base of the leaf, and its lower end is connected with the branch.The main function of the petiole is to dredge and support. The petiole can twist and grow, thus changing the position and direction of the leaves, so that the leaves do not overlap each other, and can fully receive sunlight. This feature is called leaf mosaic.[3]
Stipule
Stipules are appendages at the base of petioles, which often grow in pairs.Its shape and function vary with plant species. In addition to protecting young leaves, some green stipules can also carry out photosynthesis.[3]
Basic type
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simple leaf
A leaf with only one leaf on a petiole is called a single leaf.Such as cotton, peach and rape.[5]
Compound leaf
Compound leaf type
More than two completely independent leaflets growing on the petiole are called compound leaves.Compound leaves are rare in monocotyledons and quite common in dicotyledons.According to the branching of the total petiole and the number of leaflets, compound leaves can be divided into the following types:[6]
Feathered compound leaves: leaflets are arranged on both sides of the total petiole in a feather shape.One terminal lobule is calledOdd pinnate compound leaf, such as black locust, wisteria, etc.Two terminal leaflets are calledEven pinnate compound leaf, such as double pod cassia, acacia, etc.Those with unbranched leaf axis are called single pinnate compound leaves, such as Robinia pseudoacacia, Wisteria wistaria, Cassia bicampullata, etc.Those whose leaf axis branches once are called double pinnate compound leaves, such as Phoenix tree, jacaranda, acacia, etc.Those whose leaf axis branches twice are called triple pinnate compound leaves, such as southern India.[6]
Palmate compound leafThe leaflets arranged at the top of the leaf axis are called palmate compound leaves, such as kapok, horse chestnut, etc.[6]
Trifoliate compound leaf: Compound leaves with only three leaflets are called triple compound leaves, such as autumn maple, wild winter jasmine, clover, etc.[6]
Single compound leafThe compound leaf with only one leaflet is called single compound leaf, such as citrus, pomelo, etc.[6]
The leaves of different plants have various shapes, sizes and shapes.But as for a plant, it is relatively stable and can be used as a basis for plant identification and classification.The size of leaves varies greatly.Some are as small as scales, only a few millimeters, such asTamarix chinensis, cypress;Large ones range from a few centimeters to tens of meters.For example, the leaf diameter of Wang Lian can reach 1.8-2.5m.[7]
The shape of leaves is mainly determined by the proportion of length and width and the position of the widest part.Common shapes include scale, strip, thorn, needle, cone, lancet, spoon, egg, oblong, diamond, heart, kidney, ellipse, triangle, circle, fan, sword, etc.[8]
Descending: The leaf base grows downward along the petiole and extends on the stem.[10]
Tapering: the two parts at the base gradually become inward curved and narrow, similar to the tapering at the leaf tip.[10]
Wedge shape: the middle part gradually narrows to both sides of the base, such as weeping willows.[10]
Cross section: The base is cut into a straight line as if cut off.[10]
Round: The base is semicircular, such as an apple.[10]
Earlobe shape: there are small lobes in the shape of earlobe on both sides of the base, such as rape.[10]
Heart shape: the connection with the petiole is concave to form a gap, and there is a round lobe on both sides, such as redbud.[10]
Oblique shape: both sides of the base are asymmetric and oblique, such as begonia.[10]
Shield: the blade is connected with the petiole at the center of the blade or at a point within the edge.[10]
Syncarpous penetrating stem: the lobes on both sides of the base of opposite leaves combine to form a whole, and the stem seems to penetrate the leaf.[10]
Arrow shaped: the lobules on both sides of the base are backward and slightly inward, such as Sagittarius.[10]
Halberd shape: the small lobes on both sides of the base protrude outward, such as a bowl flower.[10]
The edge of the leaf is called leaf edge, and the common forms are:[10]
Full edge: the leaf edge is smooth without any teeth or notches, such as magnolia, wintersweet, wisteria, etc.[10]
Serrated: The leaf margin has sharp serrations, and the tooth end is forward, such as sweet clover.[10]
Double sawtooth: there are sawtooth edges, such asOriental Cherry, Di Tang, etc.[10]
Blunt tooth: The tooth with blunt head on the leaf margin, such as Euonymus japonicus.[10]
Teeth: Sharp teeth, with tooth ends outward, almost 90 degrees.[10]
Wavelike: The edge undulates like a small wave, like a cigar.[10]
Notch: The concave and convex leaf edges with larger and deeper wing edges are called nicks.According to the number and arrangement of lobes, they can be divided into three lobes, pinnate lobe and palmate lobe;It can also be divided into shallow fissure, deep fissure and complete fissure according to the depth of the lobes.[10]
The distribution of leaf veins in the leaves is called venation, and the common ones are as follows.[11]
Parallel venation: the lateral venation is parallel or nearly parallel to the midvein and reaches the top of the leaf, or runs parallel to the leaf margin from the midvein.It is the venation type of monocotyledon, such as wheat, rice, palm, etc.According to the different arrangement, it can be divided into straight parallel veinsLateral parallel vein, emitting parallel veins and arc-shaped parallel veins.[12]
Reticular venation: It is the venation type of dicotyledon, which is mainly characterized by the interconnection of small branches of leaf veins into a network.It also includes pinnate reticulate veins and palmate reticulate veins.In the middle of the former, there is an obvious main vein with many lateral veins on both sides, and between the lateral veins there are many fine veins, such as peach and pear;The leaves of the latter have several thicker veins from the leaf base, which radiate to the leaf edge and form a network of multi-level branches, such as grapes and cotton.[12]
Fork venation: Each leaf vein has multi-level bifurcated branches, which is a relatively primitive venation, such as ginkgo.[12]
Three veins: there are three obvious veins at or near the base of the leaf, called three veins.Such as Indian cinnamon, cinnamon, and simple tree.[13]
That is, the arrangement pattern and rule of leaves on stems or branches.Common ones are:
Mutualism: Each node has only one leaf, such as camphor, camellia, rose, wisteria, etc.[13]
Opposite: Two leaves are planted in each section, such as sweet clover, wintersweet, and Lingxiao.[13]
Rotation: Three leaves or more are born at each node, such as oleander.[13]
Cluster: the internode is extremely shortened, and most leaves are clustered on short branches, such as ginkgo, cedar, larch, etc.[13]
Basal: The leaves send out from the base of the earth's surface in the form of rosettes and are called basal, such as gerbera, hyacinth, ophiopogon japonicus, etc.[13]
Leaf metamorphosis
The leaves of plants are often subject to many metamorphosis due to different types and the impact of the external environment. Common metamorphosis includes:[13]
Insect catching leaves: Some plant leaves are metamorphosed and can catch insects. Such metamorphosed leaves are called insect catching leaves.For example, the petiole of pitcher plant is very long, the base is a flat pseudo leaf, the middle is slender like a tendril, which can wind other things, and the upper part becomes a bottle shaped insect trap. The leaf is born at the mouth of the bottle and forms a small cap on the mouth of the bottle.There are many glands in the bottom of the bottle, which can secrete digestive juice to digest and utilize the fallen insects.[13]
Scaly leaf: The leaf metamorphoses into scales, called scaly leaf.There are three kinds of scales: one is the scales outside the buds of woody plants, also called bud scales;The other is the degenerated leaves on the underground rhizome - scale leaves or scales;The other is the fleshy, plump and storage scale leaves on the bulbs of lilies and onions.[13]
Leaf tendril: a part of a leaf becomes tendril like, called leaf tendril.Suitable for climbing growth.For example, 2~3 pairs of leaflets at the top of pea compound leaves become tendrils.[13]
Bracts (bracts): The abnormal leaves under the flowers are called bracts (or bracts), for example, the epicalyx outside cotton is called bracts.The bracts which are numerous and gather at the periphery of the inflorescence are called the involucre, such as the involucre outside the sunflower inflorescence.Bracts or involucres protect flowers and fruits.The bracts have bright colors, such as poinsettia.[13]
Leaf thorns: The leaves or some parts of the leaves of this plant are metamorphosed into thorns, which are called leaf thorns. For example, the stipules of black locust and wild jujube are metamorphosed into hard thorns,CactusSome plants have stiff spines on flat fleshy stems.[13]
Leaf color diversity
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Generally speaking, the molecular ratio of chlorophyll to carotenoid in normal leaves is about 3:1, which makes the leaves appear green. However, when leaves fall, the color of the leaves changes due to this ratio or the presence of anthocyanins, which is particularly important for enriching the color of ornamental plants and improving the ornamental value.In addition to normal green, leaf color can be divided into the following categories:[14]
Colored new leaves: the new young leaves present bright colors.For example, young leaves of Hedysarum paniculatum, Geranium japonicum, Pistacia chinensis, Photinia serrulata are red or purplish red;Ligustrum lucidumThe new leaves of Euonymus aurea, Euonymus aurea, etc. are golden yellow.[14]
Autumn leaves: The leaves change color in autumn every year, which lasts for a long time and has high ornamental value.For example, the autumn leaves of Acer negundo, Liquidambar formosana, Phyllostachys triangularis, Metasequoia glyptostroboides, Cotinus coggygria are red or purplish red;The autumn leaves of Ginkgo Goose Feet, Platanus acerifolia and Lysimachia roxburghii are yellow or yellowish brown.[14]
Constant color leaves: some ornamental plant varieties, whose leaves are always in different colors, are called constant color leaf trees.Such as red leaf plum, purple leaf peachberberis thunbergii , etc. are red or purplish red throughout the year;Forsythia fortunei, golden leaf maple, golden cypress, golden leaf banyan, etc. are yellow or golden all the year round.[14]
Speckled leaves: leaves with spots, patches or stripes of other colors, forming mottled color lines such as gold edge, gold core, silver edge, silver core, sprinkling gold, etcPelargonium zonale , golden peach leaf mountain lake, flower leaf goose palm vineAlpinia zerumbet 、Ivy, flower leaf banyanSilver Vein Grass, colorful leafy grass, etc.[14]
Leaf structure of dicotyledon
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The leaves of angiosperms are flat, forming large photosynthetic and transpiration areas.Because the upper and lower surfaces receive different light, the internal structure is also different.Generally, the light facing side is called the upper surface or paraxial surface or web, and the opposite side is called the lower surface or abaxial surface or back.Generally, the internal structure of leaves is divided into three parts: epidermis, mesophyll and vein.[15]
epidermis
The epidermis originates from the original epidermis and covers the surface of the whole leaf. It can be divided into upper epidermis and lower epidermis. The adaxial surface is the upper epidermis and the abaxial surface is the lower epidermis.The epidermis of most plant leaves is composed of a layer of cells, such as cotton and privet;The epidermis of a few plants consists of multiple layers of cells, such asIndian rubber tree, oleander, etc.The epidermis is mainly composed ofEpidermal cell, stomatal apparatus and trichome.[15]
mesophyll
The mesophyll is distributed between the upper and lower epidermisBasic meristemIt is mainly composed of assimilating tissues, and may also have secretory cavities, heterocytes with crystals, and stone cells.Mesophyll cellIt is rich in chloroplasts and is the main place for photosynthesis.Due to the different light conditions on the back and belly of the leaf, the mesophyll cells of dicotyledon differentiate into palisade tissue on the adaxial (ventral) surface and sponge tissue on the abaxial (back) surface. Leaves with such mesophyll tissue structure are called bifacial leaves or bifacial leaves, such as those of cotton and privet.Some dicotyledonous plants have no differentiation of palisade tissue and sponge tissue in their mesophyll, or have differentiation of palisade tissue in their upper and lower epidermis, which is called isoplanar leaves, such as the leaves of lemon and oleander.The color of the degree surface of the leaves on both sides is deep and the color of the back surface is light, while the color of the back and ventral surface of the leaves on the same side has little difference.[15]
vein
Leaf veins are vascular bundles in the leaves, which are developed from the procambium. There are also vascular bundles in the east of the main veins and larger lateral veinsParenchymaAnd mechanical organizationBasic meristemDeveloped.The main function of leaf veins is to transport water, inorganic salts and nutrients, and to provide mechanical support for leaves.The leaf veins of dicotyledonous plants are mostly reticulate veins. There is one thickest leaf vein on the central longitudinal axis of the leaf, called the midvein. The smaller branches from the midvein are lateral veins. The lateral veins then branch into smaller veinlets, and the end of the veinlets is called the vein tip. Therefore, the vascular bundles in the dicotyledonous leaves form an interconnected network system parallel to the leaf surface on the central plane of the leaves.[15]
Leaf structure of gramineous plants
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The leaves of gramineous plants are also composed of epidermis, mesophyll and vein. The structure of each part is different from that of dicotyledons.[15]
epidermis
The structure of leaf epidermis of gramineous plants is complex.exceptEpidermal cellIn addition to stoma apparatus and surface fur, there are alsoVesicular cell。[15]
mesophyll
The mesophyll of gramineous plants, without differentiation of palisade tissue and sponge tissue, is called isohedral leaf.Of various gramineous cropsMesophyll cellThere are different characteristics in morphology, even the morphology of mesophyll cells in leaves of different varieties or different parts of plants is slightly different.For example, in rice mesophyll cells, the cell wall is folded inward, but it is flat and round as a whole, stacked along the longitudinal axis of the leaf, and chloroplasts are distributed along the regular pattern of the cell wall;In the mesophyll cells of wheat and barley, the cell walls are folded inward to form a structure with "peak, valley waist and ring", which is conducive to more chloroplasts being arranged at the cell edge and easy to accept COtwoAnd light for photosynthesis.[15]
vein
The leaf veins of gramineous plants are parallel veins, and the midvein is obviously large, similar to the vascular bundle structure in the stem. The lateral veins are uniform in size and parallel to each other.Vascular bundles areLimited vascular bundleThere is no cambium.The arrangement of xylem and phloem is similar to dicotyledon.There are 1~2 layers of cells surrounding the vascular bundle to form vascular bundle sheath. In plants with different photosynthetic pathways,bundle sheath cells There are obvious differences in the structure of.[15]
Ecological type
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Leaves are the most sensitive organs in plants, and their morphological structure is most likely to change with different aspects of ecological conditions to adapt to the environment.In various ecological conditions, water and light have the greatest impact on leaf morphological structure.[16]
According to the different water requirements of plants, plants are divided into xerophytes, mesophytes and aquatic plants;Plants are divided into positive plants, neutral plants and negative plants according to their different requirements for light.[16]
physiological function
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Leaves are the main organs of green plants for photosynthesis and transpiration, and also have the functions of absorption, reproduction and storage.[17]
photosynthesis
Green plants can absorb sunlight energy (mainly in leaves)carbon dioxideThe process of synthesizing organic substances with water and releasing oxygen is called photosynthesis.Photosynthesis is the basis of all material metabolism and energy metabolism in the organism, and plays a unique role in various metabolic pathways.It is of great significance to the ecological balance of nature and human survival.[17]
Transpiration
It is the process of water loss from living plants to the atmosphere in the form of gas.It has positive significance in plant life: the first transpiration is one of the driving forces of root water absorption;Secondly, the minerals absorbed by roots mainly rise with the transpiration flow, and transpiration is beneficial to the movement of mineral elements in plants;Third, transpiration can reduce the surface temperature of leaves, so that leaves will not be damaged by excessive temperature under strong sunlight.[17]
Absorption and secretion
For example, fertilization outside the root, that is, spraying a certain concentration of fertilizer on the leaves, is to use the absorption of leaves.Another example is pesticide spraying (such asOrganophosphorus insecticide）And spraying herbicides, also through the leaf surface absorption into human plants and play a role.[17]
Reproductive function
The leaves of some plants can reproduce, and adventitious roots and buds can be formed at the veins on the edge of the leaves.When they separate from the parent leaves, they can form new plants independently.For example, ground-based rooting means that adventitious buds with adventitious roots grow along the veins at the edge of the leaves, and when they fall off from the mother body, new plant bodies can be formed.This physiological function of leaves is often used to reproduce certain plants.For example, when breeding citrus, lemon and begonia, leaf cutting can be used;Leaves also have the function of storing nutrients, such as onion, lily, garlic and other scales.[17]
