Fruits, flowers and leaves of the orange ( Citrus × sinensis )
The citrus plants ( Citrus ) are a genus of plants from the diamond family (Rutaceae). They come from the tropical and subtropical southeast of Asia . The representatives of this genus supply the citrus fruits (mainly oranges , mandarins , lemons and grapefruits ), which are widely grown in the warm regions of the world. These fruits are a special form of the berry that is characteristic of the Citrus genus .
Branches, trunk and roots
The young twigs are green and angular. They have a ridge below each leaf base that slowly tapers down. The result is a triangular cross-section, which, however, disappears as the thickness increases . In the leaf axil there are buds and sometimes a thorn each . Thorns are often only formed in young plants or strongly growing branches. The buds that sprout can develop into purely vegetative sprouts, sprouts with leaves and flowers, or those with flowers only. The branches do not end their growth in length with an end bud, the last side bud takes over this function ( sympodium ).
Older branches are round, their bark is thin, gray and smooth, the wood is yellowish. The trunk is often crooked and divides into many irregularly branched branches just above the ground. Under favorable conditions, there is no pause in growth; annual rings are only formed in climates with unfavorable seasons. The growth in thickness can take place in several phases during a growth period, so that xylem and phloem form structures several times a year that resemble annual rings.
The root system consists of a tap root and lateral secondary roots. Two types of roots can be distinguished: thicker retaining roots, which also have a secondary growth in thickness, and thinner fiber roots, which form branched tufts, but hardly thicken. Fungi of the genus Glomus have been discovered as mycorrhiza .
The foliage leaves in the genus Citrus are understood as a reduction in unpaired pinnate leaves in which only the terminal leaflet is present. Only in closely related genera are three leaflets formed. There is separating tissue between the petiole and the shoot and less developed between the petiole and the leaflet. The leaves are arranged in a spiral on the branches . After three revolutions, the ninth leaf is exactly above the first, sometimes even after two revolutions the sixth leaf. With each new shoot, the direction of the spiral changes.
The leaf blade is oval to elongated, the tip of the leaf sometimes tapering into a trickle tip . The leaves are dark green on the upper side, lighter yellow-green on the underside, and smooth on both sides. The leaf margin is usually slightly notched. The leaves are usually thick and leathery to the touch. Of the leaf veins , only the main vein protrudes in the middle of the leaf, the side veins branch out in a Y-shape, the side branches of adjacent veins meet ( anastomosis ) and form a reticulate vein. There are oil glands in the leaf, mainly on the edge and at the tip of the leaf. In the backlight they can be seen as small bright spots.
The petiole is often clearly winged, in some species the widened petiole can be just as large as the actual leaf blade.
Inflorescences and flowers
The flowers sit individually or in small numbers together in umbel- like racemose inflorescences . Flowers or inflorescences develop from buds in the leaf axils of the branches, the inflorescences can be leafy or leafless. Depending on the growth rhythm, citrus plants bloom at a certain time of the year, often immediately after an unfavorable season, or even spread over the whole year.
There are hermaphrodite and purely male flowers. The stalked, radial symmetry flowers have a diameter of 1 to 5 centimeters. The sepals are fused and form a five-lobed, fleshy calyx. It sticks until the fruit is ripe. The petals , usually five, are not fused. They are thick and leathery, with a waxy smooth surface, colored white or rarely pink on the outside. The petals contain oil glands.
Stamens are usually four times as many as petals, i.e. twenty, but there are also up to forty. The white stamens can be grown together in several groups at the base. The yellow anthers are four-lobed.
There is a nectar disc at the base of the stamens . This ring-shaped structure encloses the gynoeceum and secretes a watery nectar . The flowers often give off a strong scent and are therefore attractive to insects and the nectar produced.
The upper ovary consists of about three to 14 fused carpels . Each carpel contains two to eight or even more ovules that are arranged vertically in two rows along the central axis. Through the individual, cylindrical stylus , stylus canals lead from the ovules to the scar . This is quite large and round.
The spherical, oval or somewhat pear-shaped fruits are formed from the ovary, divided into segments ("columns", "slices") according to the number of carpels. The fruit size varies greatly, the smallest fruits have a diameter of about one centimeter, the largest cultivated varieties produce fruits with a diameter of thirty centimeters.
The pericarp (fruit wall) forms three distinguishable layers: The exocarp, here called flavedo, forms the outermost, colored layer of the fruit, with a cuticle and densely packed parenchymal cells . Here are again numerous oil glands. The parenchymal cells contain chloroplasts , which are responsible for the green color of unripe fruits. In the course of ripening, these transform into chromoplasts that turn the fruit yellow or orange. The mesocarp ( albedo ) below is white and spongy. The albedo degenerates to different degrees depending on the species, as do the partition walls (septa) of the ovary. Accordingly, some citrus fruits can be easily peeled and divided into individual segments. The endocarp consists of a thin membrane that extends around the individual carpels.
From the endocarp, small, juice-filled sacs turn inward into the individual segments and fill them completely. These sacs grow from the outside of the fruit towards the center of the fruit, the outer ones are short stalked, and the stalks become longer inward. They are encased in an epidermis so that the individual sacs can be seen, but mostly grown together in such a way that they cannot be separated. Inside these sacs there are large cells with large vacuoles , but some smaller cells and oil droplets can also be found there. The entirety of the sacs is called the pulp.
These structures, rich in aromatic, sweet to bitter juice, are the part of the fruit that is consumed fresh. The surrounding cellulose-rich white tissue is fiber for digestion, the oil-rich peel is - if insecticide-free - grated, candied as a spice or used to extract the flavor.
The central axis (columella) of the fruit, which extends from the base of the flower stalk on one side to the base of the stylus on the other, is filled with spongy parenchymal tissue and ducts. The carpels have grown together here in the middle; in the middle of each carpel, i.e. in the center of the fruit, is the attachment point of the style canal to the ovules. In the ripe fruit, the central axis can be filled with tissue or hollow.
The interface between the flower and the flower stalk becomes lignified as the fruit ripens. While the flower still has a separating tissue between the flower stalk and ovary, this becomes solidified when a fruit forms. At maturity, a new predetermined breaking point forms.
This special form of a berry described is sometimes called hesperidium , an expression that Carl von Linné coined. He was referring to the "golden apples of the Hesperides ". Other botanical terms for these leathery-skinned berries are endocarp berries or armored berries .
In the case of oranges and grapefruit, the harvest is usually either totally, i.e. H. all fruits of a tree are harvested at the same time, or gradually, as with lemons and limes. The fruits do not ripen (like bananas) because they are poor in starch. Ripe and full skin color are not always achieved at the same time. Green-skinned therefore does not always mean immaturity. A few cool nights are required for the usual coloring. Warm weather causes green spots.
The seeds are round to oblong-pointed and about 0.5 to 1 centimeter in size. Their straw-colored outer shell (testa) is hard and leathery, often with ridges or ribs. Below is a brown-colored, dry skin. In the ripe seed, the space is filled by the cotyledons , there is no endosperm . The cotyledons store the nutrients for the seedling and are colored white, yellowish or green depending on the species.
Each seed can contain several embryos ( polyembryony ), a rarity among seed plants. However, most of the embryos of a seed wither except for one. The polyembryony arises from the fact that an embryo is created not only from the fertilized egg cell of the ovule, but also from individual nucellus cells of the ovule. This nucellar embryony is a special form of apomixis . For the formation of these embryos, however, the fertilization of the egg cell is necessary as a trigger. Thus some of the embryos, often even the larger one, correspond genetically to the mother plant, and only some have two parents.
If the flowers are not pollinated, some citrus plants will still produce fruit (virgin fruit). These then contain no seeds, not even those with nucellar embryos. Some varieties seldom or never seed even after the flowers have been pollinated. Commercially used varieties are selected for those fruits without seeds. (Example: Persian lime, Satsuma mandarin)
Genetic , phylogenetic and biogeographic analyzes of citrus plants were interpreted to mean that it originated some eight million years ago in the area of the southeastern foothills of the Himalayas , had in a region that today's eastern Assam , the north of Myanmar and the West of Yunnan covers , and that at that time - in the Miocene - they very quickly split into various types. Due to the edible fruits, citrus plants were cultivated and distributed early on and can be found worldwide.
Origins in East Asia
The forerunners of the edible citrus fruits are believed to be on the southeastern slope of the Himalayas, the present-day area of northeast India, Myanmar and the Chinese province of Yunnan . Citrus fruits are mentioned very old in the Yü Kung , which records tribute payments to the Chinese ruler Ta Yu , who ruled from 2205 to 2197 BC. BC (the text, however, is dated to around 800 BC). Legge translates from this:
“The wild people of the islands brought garments of grass, with silks woven in shell patterns in their baskets. Their bundles contained small oranges and pummeloes, - rendered when specially required. "
“The natives of the islands brought clothes made of grass with silk shell designs in their baskets. Their bundles contained small oranges and grapefruits - brought on special request. "
The word “chu” meant small tangerines and kumquats, with “yu” grapefruits and yuzu . Only later, around 200 BC. BC, "kan", larger mandarins or oranges, are added. Not until 300 AD are there any references to the citron in China. In 1178 Han Yen Chih was able to describe 28 different cultivated varieties in detail in the Chü lu , a monograph on citrus fruits. The grafting of citrus plants on the three-leaved bitter orange "chih" ( Poncirus trifoliata ) was also known.
In India there is a mention of citrus in Vajasaneyi samhita , texts dating back to 800 BC. Were written. Lemon and lemon are called jambila there. Names for the orange appear around the year 100 AD.
Introduction to Europe
The lemon was the first citrus fruit to be spread westward by humans. As a result of Alexander the Great's traits , the tree that was cultivated in Persia at the time was introduced into Asia Minor . Theophrastus gives around 310 BC A detailed description of the lemon and its use, but also indicates that he does not know the fruit firsthand. It was then generally known in the eastern Mediterranean in the second century AD. They were introduced by Jewish migrants who, after the conquest of Jerusalem in AD 70, settled in Spain, Greece and Italy, especially in Calabria . Virgil calls the fruit Median apple , and Dioscurides then uses the Latin name citria . Pliny (77 AD) calls the citron lemon malus medica , malus assyria , or citrus , according to his description it was only known to the Romans as an exotic import at that time, any trees in Italy probably did not bear fruit. In De re coquinaria , a collection of late antique Roman recipes from the 3rd or 4th century AD, a method for storing lemons for longer is mentioned, among other things. A sauce recipe is also described in which the lemon peel is mixed with mint and fennel as well as broth. Although the citron is not explicitly mentioned in the Bible (the word hadar may refer to it), it plays a prominent role in Jewish symbolism and appears on Jewish coins from AD 66 to AD 70.
The next dive citrus lemon and bitter orange ( sour orange ) on Roman mosaics, such as the Mausoleum of Constantia , daughter of Constantine (about 330 n. Chr.). The exact assignment of the fruits shown is uncertain. What is certain is that with the Arab conquests in the 9th century, Arab settlers also began to cultivate bitter oranges and lemons in the conquered European regions. Ibn Hauqal , who also visited Sicily on his long travels, describes, for example, in his book about the image of the earth , written down in 977, the extensive gardens in which orange and lemon trees grew due to the irrigation methods introduced.
The well-known cultivated citrus fruits reached a similar range as in China. Around 1500 lemon, lemon, lime , grapefruit and bitter orange were known in the Mediterranean region . The Portuguese explorers came across lemons and bitter oranges in East African gardens of Arab traders on their way to India. They also brought the sweet orange to Europe.
In the 18th century, lemon traders (as competitors of the local spice traders and spice dealers) sold their goods on southern German markets, such as the "Tyroler Lemon Men". The commodities of the so-called lemon men not only included citrus fruits such as lemons, limes and bitter oranges, but also lemon peel, pomegranates, figs, bay leaves, pistachios, walnuts, almonds, Parmesan cheese, marinated fish, olives, raisins, Italian sausages, Venetian soap, Italian wines , Gut strings, Genoese gloves and much more.
It was not until 1805 that the mandarin was imported from China. A little earlier, the Barbados grapefruit, a cross between grapefruit and orange, became known. Kumquats were presented to the Royal Horticultural Society in London in 1846 by Robert Fortune .
The name citrus goes back to the Latin word citrus , which was used to describe different plants: on the one hand an aromatic wood, which was probably cedar wood and wood of the articulated cypress , on the other hand the citron ( Citrus medica ). The name was therefore transferred from the Greek word kédros for cedar to the citron. What these plant species had in common was their use as a fragrance supplier and moth repellent.
It was not until the end of the 14th century that the word was transferred to another, then more important citrus plant: the lemon ( Citrus × limon ). Carl von Linné then used the term citrus in 1753 for the entire genus. Agrumen (ital .: agrumi , sour fruits ) is a collective name for the fruits of the citrus plants.
Many names for individual representatives of the citrus plants come from Arabic, see the articles on the respective plants.
The different citrus fruits have been assigned the most varied of meanings over their wide distribution area.
In China, a form of citron where the segments have grown together on one side and spread out like fingers on the other is known as the Buddha's hand . It can be understood for wealth, as a gesture of grasping and further as a symbol for corruption. The large number of seeds leads to the concept of fertility, which was closely linked to that of wealth. Etrog , another form of the citron, is important in Jewish religious rituals, such as the Feast of Tabernacles , along with palm, willow and myrtle.
In Europe, citrus fruits were first considered a supplier of fragrances, a means of repelling insects and medicine. Lemon peel often appeared as part of recipes for plague medicine. They were often linked to death in some way: for example, those condemned to death carried a lemon in their hands on their way to execution, as did the mourners at funerals. In painting Mary is depicted with a citrus fruit, in profane art she is a symbol for the deceased.
Since the citrus fruits were an expensive import product in Central Europe, they were also important as a symbol of luxury and wealth. An impressive example of this are the baroque Hesperides gardens laid out by the patricians in Nuremberg. The internationally active merchant and botanist Johann Christoph Volkamer had his citrus plant collection engraved and colored in copper by several artists under the title Nürnbergische Hesperides at the beginning of the 18th century . With the increasing use as food, away from the medical aspect, they are represented on painted dishes. Together with other imported fruits, they represent the exoticism of foreign countries.
The main use of the fruits is as food. As fruit, the fruits are eaten raw, around a third are processed into juice and other products. As a food, citrus fruits are best known for their high levels of vitamin C and minerals . The fruit trade calls mandarins , clementines , satsumas , many tangelos and tangerines as easy peelers (from English easy = simple and to peel = peel ), because the peel of these citrus fruits can be easily removed from the pulp. Citrus fruits do not ripen after harvest and are therefore classed as non-climacteric fruits . They are also sensitive to cold, below 2 ° C they become bitter. The ideal storage is at 7 ° C and high humidity.
The essential oils formed in the glands of the outer shells also make them interesting for seasoning and fragrances. There is a special household appliance for the kitchen, the zest ripper (sometimes also known as a zester ), which is used to cut off wafer-thin strips of the outer shell, so-called zests . The outer peel is also made into lemon peel and jam, and kumquats are eaten whole in a similar way. The juice of sour citrus fruits is used less pure, but also for seasoning. The leaves of the kaffir lime are added to the meal as a spice, similar to bay leaves. In Arabic cuisine, dried limes are known as an ingredient for seasoning.
Essential oil is also extracted from the flowers and is sold as neroli oil .
The peel of citrus fruits is often treated with waxes (e.g. made from polyethylene wax , beeswax or shellac ) to which preservatives such as thiabendazole (E 233), orthophenylphenol (E 231), sodium orthophenylphenol (E 232), biphenyl (E 230) and imazalil are added . In 2017, the Lower Saxony State Office for Consumer Protection and Food Safety (LAVES) was able to detect pesticide residues in almost all citrus fruits sampled . The limit value was exceeded in around 3.4% of the samples.
Citrus fibers are used as an additive in the food industry.
This genus is of commercial importance as the plants are cultivated for their fruits. The world harvest in 2018 was around 95 million tons.
|Important producers of citrus fruits 2018 (in t)
The largest producers are highlighted in gray
|country||Oranges||Mandarins 1||Grapefruit 2||Lemons 3||total|
|People's Republic of China||9,103,908||19,035,444||4,965,768||2,482,884||35,588,004|
Citrus plants grow in warm regions, for example around the Mediterranean . However, there are also plants that can tolerate temperatures as low as −12 degrees Celsius. They are mainly cultivated in the so-called citrus belt between the 20th and 40th parallel north and south of the equator . Since the citrus fruits take a long time to ripen, a long, warm summer is required; this limits cultivation in cooler climates. In arid areas like the Mediterranean basin, irrigation is necessary. Citrus plants grow well in the ever-humid tropical areas, but several factors prevent commercial use. Most varieties tend, in a climate without a dry or cold period, to continually grow small amounts of fruit that cannot be harvested efficiently. The skin of the fruit is often not very colorful under tropical conditions, and it is often attacked by fungi.
Problems and diseases
A whole range of organisms feed on citrus plants and are therefore perceived as pests in commercial cultivation. Since the cultivation is often carried out in monoculture , problems with the rapid spread of the pests and the rapid growth of the pest populations arise during control - as with other cultivated plants.
More than 250 different insects have been found on citrus plants. Some who specialize in citrus plants and are particularly pests in their cultivation are the citrus leaf flea ( Diaphorine citri ), black flies ( Aleurocanthus woglumi ), white flies ( Dialeurodes citri , Aleurolobus citriifolia and others), scale insects ( Aonidiella aurantii , Aonidiella citrina ), mealybugs ( Planococcus citri ) and aphids ( Toxoptera citricida , Toxoptera aurantii ). The larvae and adult animals suckle plant sap, and fungi settle on the honeydew excrement. Viral diseases are also transmitted. The larvae of the citrus leaf miner ( Phyllocnistis citrella ) live in young leaves. Citrus thrips ( Scirtothrips spp., Heliothrips haemorraeodalis ) and citrus mites ( Eutetranychus orientalis , Eutetranychus banksi , Tetranychus fijiensis ) suck plant juices. Fruit-eating moths ( Ophederes spp., Achaea janata ) feed on unripe fruits, which then rot and fall off. The caterpillars of several species of the genus Papilio feed on citrus plants, some of which, such as z. B. Papilio demoleus , can cause considerable damage. The moths of a species of moth ( Inderbela quadrinotata ) lay their eggs on the bark. The larvae feed under the bark.
Fungi such as Phytophthora citrophtora and other Phytophthora species usually infect plants via the roots, especially when the soil is very wet. Spores get to different parts of plants through rainwater, where they attack both wood and leaves or fruits. The susceptibility of the plants can be reduced by selecting suitable supports. Fusarium fungi also attack the roots, Pellicularia salmonicolor trunk and branches. Various types of powdery mildew ( Acrosporium tingitaninum , Colletotrichum gloeosporioides , Botryodiplodia theobromae ) and scab ( Elsinoe fawcettii ) can be found on the leaves and young twigs .
Citrus cancer ( Xanthomonas axonopodis cv. Citri ) is triggered by bacteria that penetrate leaves, twigs and fruits through tiny injuries . Round, gray spots form, if the infestation is severe, the leaves and twigs die off, and infested fruits can no longer be sold. " Citrus Greening " is triggered by Liberobacter bacteria, which are spread by leaf fleas and inhabit the phloem of the plants.
Viruses are also found in citrus plants, such as the citrus tristeza virus (CVD), citrus exocortic viroid (CEVd), mosaic and ring spot virus. Virus-free plants can be grown through in vitro propagation.
If citrus plants are cultivated in an area for a long time, young plants will no longer grow well ( reproduction problems ). This can partly be attributed to an increased number of harmful fungi in the soil, but at least bitter oranges and probably other species excrete substances that inhibit the growth of other plants ( allelopathy ). Depending on which variety is to be replanted, this can also be sensitive to it.
For citrus plants, the 18 chemical elements are necessary as nutrients that are generally required for the growth of green plants. Since the growth and the harvest quantity of citrus fruits can be seriously impaired in the case of a lack of nutrients, nutrient analyzes are often carried out on the citrus plantations in Florida , for example, from the leaves of citrus trees in order to be able to identify and remedy corresponding deficiencies in good time.
|nutrient||Appearances in case of deficiency|
|Nitrogen (N)||Growth retardation, reduced flowering, light green discolored leaves (symptoms are similar to those of magnesium deficiency)|
|Phosphorus (P)||Growth retardation, older leaves lose their dark green color, fall off prematurely, fruits fall off prematurely|
|Potassium (K)||Growth retardation, yellow-colored leaf tips and margins, increased sensitivity to drought and cold|
|Boron (B)||Fruits fall off prematurely, ripe fruits are smaller, have hard skins and possibly brown spots on the inside, leaves are thickened, show chlorosis , have rolled down|
|Chlorine (Cl)||no known deficiency symptoms in citrus plants|
|Magnesium (Mg)||Ripe leaves close to the fruit show irregular yellow spots that increasingly spread to both sides of the midrib, affected leaves fall off more easily|
|Calcium (Ca)||Yellow discoloration of the leaf areas between the leaf veins, especially in the winter months, smaller and misshapen fruits|
|Sulfur (S)||Chlorosis in young leaves, not just in old ones|
|Iron (Fe)||Chlorosis especially on young leaves, the leaf veins are greener, iron deficiency often occurs in combination with zinc and manganese deficiency|
|Copper (Cu)||Unusually strong, dark green foliage, often with a raised central rib, later the branches defoliate, brown spots on the fruits, hardened skin|
|Zinc (Zn)||Light green flat lightening of the leaves, while the leaf veins themselves remain dark green|
|Manganese (Mn)||Blotchy yellowish lightening of the leaves between the leaf veins, which themselves remain green, smaller and fewer fruits|
|Molybdenum (Mb)||Development of larger chlorotic spots between the leaf veins in the summer months, affected leaves often fall off later|
|Nickel (Ni)||Death of the leaf tips, yellow discoloration of the leaf margins|
Linnaeus introduced in 1753 the genus Citrus and named five representatives (in brackets are the names used by Linnaeus): citron ( Citrus medica (), Lemon Citrus medica var. Limon ), bitter orange ( Citrus aurantium ), sweet orange ( Citrus aurantium var. Sinensis ) and grapefruit ( Citrus grandis ).
Within the diamond family (Rutaceae), the genus Citrus belongs to the subfamily Aurantioideae. This is subdivided into the tribe Clauseneae and Citreae, the further subdivision into subtribes is not supported by recent studies. The sister group of Citrus is believed to be in the genera Atalantia , Limonia and Severinia . Other related genera in the tribe Citreae include Citropsis , Pleiospermium , Feroniella , Merillia , Murraya and Triphasia . The last common ancestor of the citrus family is estimated to have lived 7 million years ago.
The delimitation of individual species within the citrus plants has long been problematic. Crosses are possible between all species. Since many of these species and varieties have been in culture for a long time, humans have spread them far beyond their natural occurrence, different species and varieties were planted next to each other in gardens and selected according to the desired fruit quality. Populations unaffected by humans only exist of species that do not produce tasty fruit.
The ability of citrus plants to form nucellar embryos that are genetically identical to the mother plant means that mutations can be passed on and otherwise sterile hybrids can reproduce. However, the resulting seedlings may look different from the mother plant, for example because young citrus plants have thorns and larger leaves. This contributed to the fact that researchers were often in the dark about the assignment of a plant - be it a specific species, a hybrid or a cultivar bred by humans.
Mutations are quite common in citrus plants, as are plants with double sets of chromosomes . The resulting variations further complicate the situation.
Swingle and Tanaka
At the beginning of the 20th century, Walter Tennyson Swingle began investigating the systematics of citrus plants. On a research trip through East Asia, he met Tyōzaburō Tanaka , who worked with him. Later, the two published independently of each other, with Swingle concentrating on describing taxa that had only naturally originated as far as possible , while Tanaka sought to capture the full diversity of citrus plants. The result was that Swingle recognized 16 species of citrus , while Tanaka classified the same plant material into 162 species.
Subsequent scientists criticized Tanaka's system for the fact that most of the species had their origin as hybrids and cultivated varieties: The indiscriminate coexistence of cultivated varieties and natural species was wrong.
Not much of Swingle's work is also valid anymore - modern methods of genetic analysis have shown that both species and genus boundaries run differently than postulated by him. However, Swingle's system had a great influence on the naming of citrus plants because of the claim to reflect natural conditions.
Due to the ease of use, a system of designations based on Swingle is also used in horticulture. The grouping is not so much based on common ancestry, but on similar fruits. Information about whether a variety, a group of varieties or a natural species is hidden behind a botanical name cannot be expected from this system. Since the old names are used in trade, here is an overview:
- Lemon ( citrus × limon lemon group)
- Citron Lemon ( Citrus medica )
- Kumquats ( Citrus japonica , Syn .: Fortunella )
The genus can be divided internally into two groups, which probably spread from the Southeast Asian mainland towards the southeast to Australia. The first group contains the citrus lemon ( Citrus medica ) and Citrus indica as well as the genera Clymenia , Eremocitrus , Microcitrus and Oxanthera, which are common to the southeast . The second group, Northeast distributed, contains the remaining Citrus species, previously under the name Fortunella severed Kumquats ( Citrus japonica ) and Poncirus .
The variety of cultivated citrus plants can be traced back to only a few species: namely the citrus lemon ( Citrus medica ), the mandarin ( Citrus reticulata ) and the grapefruit ( Citrus maxima ). These three are also by no means known from natural sites, but rather represent forms selected by humans as we know them. Only a few other species are known from nature for which it is always in doubt whether they are not garden refugees or at least by gene -Exchange with neighboring cultivated varieties were influenced. The parents are only known with certainty in the case of newer breeds; in the case of traditional varieties, these can only be determined through genetic studies.
It is assumed that the following species were not created by crossing:
- Citrus celebica Coord. - Celebes
- Citrus halimii B.C. Stone - Thailand, Malaysia, Borneo
- Citrus hystrix DC. - Kaffir lime - Malaysia, Indonesia
- Citrus ichangensis Swingle - Ichang-Papeda - South China
- Citrus japonica Thunb. - Kumquat - Southeast China
- Citrus latipes (Swingle) Tanaka - Northeast India
- Citrus macroptera Montrouz. - Malaysia, Indonesia
- Citrus maxima (Burm.) Merr. - Grapefruit - Southeast Asia (Malaysia)
- Citrus medica L. - Citron Lemon - Northeast India, Myanmar
- Citrus micrantha Wester - Philippines
- Citrus reticulata Blanco - Mandarin
- Citrus tachibana (Makino) Tanaka - possibly wild form of the mandarine - Taiwan, southern Japan
- Citrus swinglei Burkill ex Harms - It was described from the Malay Peninsula
The commercially used varieties go back to crossbreeding, so all varieties that go back to the same parents get a common name. They can be further divided into groups of varieties.
Citrus × aurantium = Citrus maxima × Citrus reticulata . The cross between mandarins and grapefruit led to both bitter and sweet oranges. Backcrosses of oranges and grapefruits gave grapefruit and pomelos. The backcrossing of mandarin and orange resulted in some of the most economically important varieties.
- Citrus × aurantium bitter orange group
- Citrus × aurantium oranges group
- Citrus × aurantium grapefruit group = Citrus maxima × Citrus × aurantium orange group
- Citrus × aurantium pomelo group = Citrus maxima × Citrus × aurantium grapefruit group
- Citrus × aurantium clementine group = Citrus reticulata × Citrus × aurantium orange group
- Citrus × aurantium Satsuma group = Citrus reticulata × Citrus × aurantium orange group
Citrus × limon = Citrus × aurantium bitter orange group × Citrus medica . Lemon and bergamot are made from the lemon and bitter orange.
- Citrus × limon Lemon group
- Citrus × limon bergamot group
Citrus × jambhiri = Citrus reticulata × Citrus medica . The following groups of varieties emerged from the crossing of mandarin and citron lemon:
- Citrus × jambhiri Jambhiri lemon group
- Citrus × jambhiri Rangpur lime group
- Citrus × aurantiifolia = Citrus micrantha × Citrus medica . From the citron and from Citrus micrantha or a closely related species, some varieties known as limes emerged.
- Citrus × junos = Citrus ichangensis × Citrus reticulata var. Austera , see Yuzu
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