Citrus

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Citrus
OrangeBloss wb.jpg
Sweet orange (Citrus × sinensis cultivar)
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Sapindales
Family: Rutaceae
Subfamily: Aurantioideae
Tribe: Citreae
Subtribe: Citrinae
Genus:Citrus
L.
Species and hybrids

Ancestral species:
Citrus maximaPomelo
Citrus medicaCitron
Citrus reticulataMandarin orange
Citrus micrantha – a papeda
Citrus hystrixKaffir lime
Citrus cavaleriei - Ichang papeda Citrus japonica - Kumquat

Contents


Important hybrids:
Citrus × aurantiifoliaKey lime
Citrus × aurantiumBitter orange
Citrus × latifoliaPersian lime
Citrus × limonLemon
Citrus × limoniaRangpur
Citrus × paradisiGrapefruit
Citrus × sinensisSweet orange
Citrus × tangerinaTangerine
See also below for other species and hybrids.

Synonyms

Eremocitrus
Microcitrus
and see text

Citrus is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes.

A genus is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses, in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.

Flowering plant Class of flowering plants (in APG I-III)

The flowering plants, also known as angiosperms, Angiospermae or Magnoliophyta, are the most diverse group of land plants, with 64 orders, 416 families, approximately 13,000 known genera and 300,000 known species. Like gymnosperms, angiosperms are seed-producing plants. However, they are distinguished from gymnosperms by characteristics including flowers, endosperm within the seeds, and the production of fruits that contain the seeds. Etymologically, angiosperm means a plant that produces seeds within an enclosure; in other words, a fruiting plant. The term comes from the Greek words angeion and sperma ("seed").

Tree Perennial woody plant with elongated trunk

In botany, a tree is a perennial plant with an elongated stem, or trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are usable as lumber or plants above a specified height. Trees are not a taxonomic group but include a variety of plant species that have independently evolved a woody trunk and branches as a way to tower above other plants to compete for sunlight. Trees tend to be long-lived, some reaching several thousand years old. In wider definitions, the taller palms, tree ferns, bananas, and bamboos are also trees. Trees have been in existence for 370 million years. It is estimated that there are just over 3 trillion mature trees in the world.

The most recent research indicates an origin of the genus in the Himalayas. [1] Previous research indicated an origin in the part of Southeast Asia bordered by Northeast India, Burma (Myanmar), and the Yunnan province of China, [2] [3] [4] and it is in this region that some commercial species such as oranges, mandarins, and lemons originated. Citrus fruit has been cultivated in an ever-widening area since ancient times.

Himalayas Mountain range in Asia

The Himalayas, or Himalaya, form a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has many of the Earth's highest peaks, including the highest, Mount Everest. The Himalayas include over fifty mountains exceeding 7,200 m (23,600 ft) in elevation, including ten of the fourteen 8,000-metre peaks. By contrast, the highest peak outside Asia is 6,961 m (22,838 ft) tall.

Southeast Asia Subregion of Asia

Southeast Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China and Japan, east of India, west of Papua New Guinea, and north of Australia. Southeast Asia is bordered to the north by East Asia, to the west by South Asia and the Bay of Bengal, to the east by Oceania and the Pacific Ocean, and to the south by Australia and the Indian Ocean. The region is the only part of Asia that lies partly within the Southern Hemisphere, although the majority of it is in the Northern Hemisphere. In contemporary definition, Southeast Asia consists of two geographic regions:

  1. Mainland Southeast Asia, also known historically as Indochina, comprising parts of Northeast India, Vietnam, Laos, Cambodia, Thailand, Myanmar and West Malaysia.
  2. Maritime Southeast Asia, also known historically as Nusantara, the East Indies and Malay Archipelago, comprises the Andaman and Nicobar Islands of India, Indonesia, East Malaysia, Singapore, the Philippines, East Timor, Brunei, Christmas Island, and the Cocos (Keeling) Islands. Taiwan is also included in this grouping by many anthropologists.
Northeast India Group of Northeastern Indian states

Northeast India is the easternmost region of India representing both a geographic and political administrative division of the country. It comprises eight states – Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, Sikkim and Tripura. The Siliguri Corridor in West Bengal, with a width of 21 to 40 kilometres, connects the North Eastern Region with East India. The region shares an international border of 5,182 kilometres (3,220 mi) with several neighbouring countries – 1,395 kilometres (867 mi) with Tibet Autonomous Region, China in the north, 1,640 kilometres (1,020 mi) with Myanmar in the east, 1,596 kilometres (992 mi) with Bangladesh in the south-west, 97 kilometres (60 mi) with Nepal in the west, and 455 kilometres (283 mi) with Bhutan in the north-west. It comprises an area of 262,230 square kilometres (101,250 sq mi), almost 8 percent of that of India, and is one of the largest salients (panhandles) in the world.

History

Citrus plants are native to subtropical and tropical regions of Asia, Island Southeast Asia, and Near Oceania, and they were first domesticated in these areas. [1] A genomic, phylogenic, and biogeographical analysis by Wu et al. (2018) have shown that the center of origin of the genus Citrus is likely the southeast foothills of the Himalayas, in a region stretching from eastern Assam, northern Myanmar, to western Yunnan. It diverged from a common ancestor with Poncirus trifoliata . A change in climate conditions during the Late Miocene (11.63 to 5.33 mya) resulted in a sudden speciation event. The species resulting from this event include the citrons (Citrus medica) of South Asia; the pomelos (C. maxima) of Mainland Southeast Asia; the mandarins (C. reticulata), kumquats (C. japonica), mangshanyegan (C. mangshanensis), and ichang papedas (C. ichangensis) of southeastern China; the kaffir limes (C. hystrix) of Island Southeast Asia; and the biasong and samuyao (C. micrantha) of the Philippines. [1] [5]

Near Oceania or Near Melanesia is the part of Oceania settled 35,000 years ago, comprising western Island Melanesia: the Bismarck Archipelago and the Solomon Islands archipelago. Compare Remote Oceania.

Assam State in northeast India

Assam is a state in northeastern India, situated south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of 78,438 km2 (30,285 sq mi). The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur to the east; Meghalaya, Tripura, Mizoram and Bangladesh to the south; and West Bengal to the west via the Siliguri Corridor, a 22 kilometres (14 mi) strip of land that connects the state to the rest of India.

Myanmar Republic in Southeast Asia

Myanmar, officially the Republic of the Union of Myanmar and also known as Burma, is a country in Southeast Asia. Myanmar is bordered by India and Bangladesh to its west, Thailand and Laos to its east and China to its north and northeast. Myanmar is the largest of the mainland Southeast Asian states. To its south, about one third of Myanmar's total perimeter of 5,876 km (3,651 mi) forms an uninterrupted coastline of 1,930 km (1,200 mi) along the Bay of Bengal and the Andaman Sea. The country's 2014 census counted the population to be 51 million people. As of 2017, the population is about 54 million. Myanmar is 676,578 square kilometres in size. Its capital city is Naypyidaw, and its largest city and former capital is Yangon (Rangoon). Myanmar has been a member of the Association of Southeast Asian Nations (ASEAN) since 1997.

Map of inferred original wild ranges of the main Citrus cultivars, and selected relevant wild taxa Map of inferred original wild ranges of the main Citrus cultivars, and selected relevant wild taxa (Fuller et al., 2017).png
Map of inferred original wild ranges of the main Citrus cultivars, and selected relevant wild taxa

This was later followed by the spread of citrus species into Taiwan and Japan in the Early Pliocene (5.33 to 3.6 mya), resulting in the tachibana orange (C. tachibana); and beyond the Wallace Line into Papua New Guinea and Australia during the Pleistocene (2.5 million to 11,000 years ago), where further speciation events occurred resulting in the Australian limes. [1] [5]

Taiwan state in East Asia

Taiwan, officially the Republic of China (ROC), is a state in East Asia. Neighbouring states include the People's Republic of China (PRC) to the west, Japan to the northeast, and the Philippines to the south. The island of Taiwan has an area of 35,808 square kilometres (13,826 sq mi), with mountain ranges dominating the eastern two thirds and plains in the western third, where its highly urbanised population is concentrated. Taipei is the capital and largest metropolitan area. Other major cities include Kaohsiung, Taichung, Tainan and Taoyuan. With 23.5 million inhabitants, Taiwan is among the most densely populated states, and is the most populous state and largest economy that is not a member of the United Nations (UN).

Japan Country in East Asia

Japan is an island country in East Asia. Located in the Pacific Ocean, it lies off the eastern coast of the Asian continent and stretches from the Sea of Okhotsk in the north to the East China Sea and the Philippine Sea in the south.

The tachibana orange is a variety of mandarin orange, a citrus fruit. It is native to China and introduced to Japan 2000 years ago. The Tanaka System assigns it to its own species, while the Swingle System places it in the same species with other mandarin oranges. Genomic analysis has shown it to be genetically pure, without the pomelo introgression found in the closely related domesticated mandarin oranges of mainland Asia, though distant enough for it to by considered a distinct subspecies by Wu, et al.. They are estimated to have diverged from other Asian mandarins about 2 million years ago, and likely spread to the islands over land bridges formed during Pleistocene glacial maxima, probably arising near where its mandarin cousins would later be domesticated in the Nanling Mountains of China.

The earliest introductions of citrus species by human migrations was during the Austronesian expansion (c. 3000-1500 BCE), where Citrus hystrix , Citrus macroptera , and Citrus maxima were among the canoe plants carried by Austronesian voyagers eastwards into Micronesia and Polynesia. [6]

<i>Citrus macroptera</i> semi-wild species of citrus

Citrus macroptera, with English common names Melanesian papeda, wild orange, cabuyao, shatkora, hatkhora, hatxora or satkara, is a semi-wild species of citrus native to Malesia, Sylhet and Melanesia.

Domesticated plants and animals of Austronesia List

One of the major human migration events was the maritime settlement of the islands of the Indo-Pacific by the Austronesian peoples, believed to have started from at least 5,500 to 4,000 BP. These migrations were accompanied by a set of domesticated, semi-domesticated, and commensal plants and animals transported via outrigger ships and catamarans that enabled early Austronesians to thrive in the islands of Maritime Southeast Asia, Near Oceania (Melanesia), and Remote Oceania, Madagascar, and the Comoros Islands.

Austronesian peoples ethnic group

The Austronesian peoples or more accurately Austronesian-speaking peoples, are a group of various peoples in Southeast Asia, Oceania and East Africa that speak Austronesian languages. The nations and territories predominantly populated by Austronesian-speaking peoples are known collectively as Austronesia.

The citron ( Citrus medica ) was also introduced early into the Mediterranean basin from India and Southeast Asia. It was introduced via two ancient trade routes: an overland route through Persia, the Levant and the Mediterranean islands; and a maritime route through the Arabian Peninsula and Ptolemaic Egypt into North Africa. Although the exact date of the original introduction is unknown due to the sparseness of archaeobotanical remains, the earliest evidence are seeds recovered from the Hala Sultan Tekke site of Cyprus, dated to around 1200 BCE. Other archaeobotanical evidence include pollen from Carthage dating back to the 4th century BCE; and carbonized seeds from Pompeii dated to around the 3rd to 2nd century BCE. The earliest complete description of the citron was first attested from Theophrastus, c. 310 BCE. [7] [8] [9]

Levant Geographic and cultural region consisting of the eastern Mediterranean between Anatolia and Egypt

The Levant is an approximate historical geographical term referring to a large area in the Eastern Mediterranean, primarily in Western Asia. In its narrowest sense, it is equivalent to the historical region of Syria. In its widest historical sense, the Levant included all of the eastern Mediterranean with its islands; that is, it included all of the countries along the Eastern Mediterranean shores, extending from Greece to Cyrenaica.

Arabian Peninsula peninsula of Western Asia situated in southern Arabia

The Arabian peninsula, simplified Arabia, is a peninsula of Western Asia situated northeast of Africa on the Arabian plate. From a geographical perspective, it is considered a subcontinent of Asia.

North Africa Northernmost region of Africa

North Africa is a region encompassing the northern portion of the African continent. There is no singularly accepted scope for the region, and it is sometimes defined as stretching from the Atlantic shores of Morocco in the west, to Egypt's Suez Canal and the Red Sea in the east. Others have limited it to the countries of Algeria, Morocco, and Tunisia, a region that was known by the French during colonial times as "Afrique du Nord" and is known by Arabs as the Maghreb. The most commonly accepted definition includes Morocco, Algeria, Tunisia, Libya, Egypt, and Sudan, the 6 countries that shape the top North of the African continent. Meanwhile, "North Africa", particularly when used in the term North Africa and the Middle East, often refers only to the countries of the Maghreb and Libya. Egypt, being also part of the Middle East, is often considered separately, due to being both North African and Middle Eastern at the same time.

Lemons, pomelos, and sour oranges are believed to have been introduced to the Mediterranean later by Arab traders at around the 10th century; and sweet oranges by the Genoese and Portuguese from Asia during the 15th to 16th century. Mandarins were not introduced until the 19th century. [7] [8] [9] [10] This group of species has reached great importance in some of the Mediterranean countries, and in the case of orange, mandarin, and lemon trees, they found here soil and climatic conditions which allow them to achieve a high level of fruit quality, even better than in the regions from where they came. [10]

The "native" oranges of Florida actually originated with the Spanish conquistadores . [11] [12] The agronomists of classical Rome already made many references to the cultivation of citrus fruits within the limits of their empire. [10] King Louis XIV of France housed citrus in orangeries, to protect the tropical fruit to be grown in the 1600s France. [13]

Name

The generic name originated from Latin, where it referred to either the plant now known as citron (C. medica) or a conifer tree ( Thuja ). It is somehow related to the ancient Greek word for cedar, κέδρος (kédros). This may be due to perceived similarities in the smell of citrus leaves and fruit with that of cedar. [14] Collectively, Citrus fruits and plants are also known by the Romance loanword agrumes (literally "sour fruits").

Evolution

The large citrus fruit of today evolved originally from small, edible berries over millions of years. Citrus plants diverged from a common ancestor about 15 million years ago, which was about when it diverged from the closely related severinia, for example the Chinese box orange. About 7 million years ago, citrus plants diverged into two groups, the main citrus genus and the ancestors of the trifoliate orange (Poncirus trifoliata), which is closely enough related that it can still be hybridized with all other citrus. These estimates are made using genetic mapping of plant chloroplasts. [15] A DNA study published in Nature in 2018 concludes that citrus trees originated in the foothills of the Himalayas, in the area of Assam (India), western Yunnan (China), and northern Myanmar. [16]

The three ancestral (sometimes characterized as "original" or "fundamental") species in the genus Citrus associated with modern Citrus cultivars are the mandarin orange, pomelo, and citron. Almost all of the common commercially important citrus fruits (sweet oranges, lemons, grapefruit, limes, and so on) are hybrids involving these three species with each other, their main progenies, and other wild Citrus species within the last few thousand years. [1] [17] [18]

Fossil record

A fossil leaf from the Pliocene of Valdarno (Italy) is described as †Citrus meletensis [19] In China, fossil leaf specimens of †Citrus linczangensis have been collected from coal-bearing strata of the Bangmai Formation in the Bangmai village, about 10 km northwest of Lincang City, Yunnan. The Bangmai Formation contains abundant fossil plants and is considered to be of late Miocene age. Citrus linczangensis and C. meletensis share some important characters, such as an intramarginal vein, an entire margin, and an articulated and distinctly winged petiole. [20]

Taxonomy

Citrus fruits clustered by genetic similarity, ternary diagram based on data from Curk, et al. (2016) Citrus tern cb simplified 1.svg
Citrus fruits clustered by genetic similarity, ternary diagram based on data from Curk, et al. (2016)
Three-dimensional projection of a principal component analysis of citrus hybrids, with citron (yellow), pomelo (blue), mandarin (red), and micrantha (green) defining the axes. Hybrids are expected to plot between their parents. ML: 'Mexican' lime; A: 'Alemow'; V: 'Volkamer' lemon; M: 'Meyer' lemon; L: Regular and 'Sweet' lemons; B: Bergamot orange; H: Haploid clementine; C: Clementines; S: Sour oranges; O: Sweet oranges; G: Grapefruits. Figure from Curk, et al. (2014). S12863-014-0152-1-3.gif
Three-dimensional projection of a principal component analysis of citrus hybrids, with citron (yellow), pomelo (blue), mandarin (red), and micrantha (green) defining the axes. Hybrids are expected to plot between their parents. ML: ‘Mexican’ lime; A: ‘Alemow’; V: ‘Volkamer’ lemon; M: ‘Meyer’ lemon; L: Regular and ‘Sweet’ lemons; B: Bergamot orange; H: Haploid clementine; C: Clementines; S: Sour oranges; O: Sweet oranges; G: Grapefruits. Figure from Curk, et al. (2014).

The taxonomy and systematics of the genus are complex and the precise number of natural species is unclear, as many of the named species are hybrids clonally propagated through seeds (by apomixis), and genetic evidence indicates that even some wild, true-breeding species are of hybrid origin.

Most cultivated Citrus spp. seem to be natural or artificial hybrids of a small number of core ancestral species, including the citron, pomelo, mandarin, and papeda (see image). [23] Natural and cultivated citrus hybrids include commercially important fruit such as oranges, grapefruit, lemons, limes, and some tangerines.

Apart from these core citrus species, Australian limes and the recently discovered mangshanyegan are grown. Kumquats and Clymenia spp. are now generally considered to belong within the genus Citrus. [24] Trifoliate orange, which is often used as commercial rootstock, is an outgroup and may or may not be categorized as a citrus.

Phylogenetic analysis suggests the species of Oxanthera from New Caledonia should be transferred to the genus Citrus. [25]

Description

Slices of various citrus fruits Citrus fruits.jpg
Slices of various citrus fruits

Tree

These plants are large shrubs or small to moderate-sized trees, reaching 5–15 m (16–49 ft) tall, with spiny shoots and alternately arranged evergreen leaves with an entire margin. [26] The flowers are solitary or in small corymbs, each flower 2–4 cm (0.79–1.57 in) diameter, with five (rarely four) white petals and numerous stamens; they are often very strongly scented.

Fruit

The fruit is a hesperidium, a specialised berry, globose to elongated, 4–30 cm (1.6–11.8 in) long and 4–20 cm (1.6–7.9 in) diameter, with a leathery rind or "peel" called a pericarp. The outermost layer of the pericarp is an "exocarp" called the flavedo, commonly referred to as the zest. The middle layer of the pericarp is the mesocarp, which in citrus fruits consists of the white, spongy "albedo", or "pith". The innermost layer of the pericarp is the endocarp. The space inside each segment is a locule filled with juice vesicles, or "pulp". From the endocarp, string-like "hairs" extend into the locules, which provide nourishment to the fruit as it develops. [27] [28]

Citrus fruits are notable for their fragrance, partly due to flavonoids and limonoids (which in turn are terpenes) contained in the rind, and most are juice-laden. The juice contains a high quantity of citric acid giving them their characteristic sharp flavour. The genus is commercially important as many species are cultivated for their fruit, which is eaten fresh, pressed for juice, or preserved in marmalades and pickles.

They are also good sources of vitamin C and flavonoids. The content of vitamin C in the fruit depends on the species, variety, and mode of cultivation. Fruits produced with organic agriculture have been shown to contain more vitamin C than those produced with conventional agriculture in the Algarve, but results depended on the species and cultivar. [29] The flavonoids include various flavanones and flavones. [30]

Acidity indicators

The Moroccan professor Henri Chapot discovered that the acidity in the more common citrons or lemons is indicated by red on the inner coat of seeds specifically on the chalazal spot, violet pigmentation on the outer side of the flower blossom, and by the new buds that are reddish-purplish. The acid-free varieties of citrus are completely lacking the red color in all the mentioned spots. [31] This designation was cited by Herbert John Webber and Leon Dexter Batchelor, the editors of the fundamental treatise on citrus, namely The Citrus Industry, which was published by the University of California, Riverside in 1967.

Cultivation

Lemons are a citrus fruit native to Asia, but now common worldwide. Lemon on a Wood Table.jpg
Lemons are a citrus fruit native to Asia, but now common worldwide.
Limes in a grocery store Limes.jpg
Limes in a grocery store

Citrus trees hybridise very readily – depending on the pollen source, plants grown from a Persian lime's seeds can produce fruit similar to grapefruit. Thus, all commercial citrus cultivation uses trees produced by grafting the desired fruiting cultivars onto rootstocks selected for disease resistance and hardiness.

The colour of citrus fruits only develops in climates with a (diurnal) cool winter. [32] In tropical regions with no winter at all, citrus fruits remain green until maturity, hence the tropical "green oranges". [33] The Persian lime in particular is extremely sensitive to cool conditions, thus it is not usually exposed to cool enough conditions to develop a mature colour.[ citation needed ] If they are left in a cool place over winter, the fruits will change colour to yellow.

The terms "ripe" and "mature" are usually used synonymously, but they mean different things. A mature fruit is one that has completed its growth phase. Ripening is the changes that occur within the fruit after it is mature to the beginning of decay. These changes usually involve starches converting to sugars, a decrease in acids, and a softening and change in the fruit's colour. [34]

Citrus fruits are nonclimacteric and respiration slowly declines and the production and release of ethylene is gradual. [35] The fruits do not go through a ripening process in the sense that they become "tree ripe". Some fruits, for example cherries, physically mature and then continue to ripen on the tree. Other fruits, such as pears, are picked when mature, but before they ripen, then continue to ripen off the tree. Citrus fruits pass from immaturity to maturity to overmaturity while still on the tree. Once they are separated from the tree, they do not increase in sweetness or continue to ripen. The only way change may happen after being picked is that they eventually start to decay.

With oranges, colour cannot be used as an indicator of ripeness because sometimes the rinds turn orange long before the oranges are ready to eat. Tasting them is the only way to know whether or not they are ready to eat.

Mediterranean Mandarin (Citrus xdeliciosa plantation, Son Carrio (Mallorca) Mandariner Citrus deliciosa.jpg
Mediterranean Mandarin ( Citrus ×deliciosa plantation, Son Carrió (Mallorca)

Citrus trees are not generally frost hardy. Mandarin oranges (C. reticulata) tend to be the hardiest of the common Citrus species and can withstand short periods down to as cold as −10 °C (14 °F), but realistically temperatures not falling below −2 °C (28 °F) are required for successful cultivation. Tangerines, tangors and yuzu can be grown outside even in regions with more marked subfreezing temperatures in winter, although this may affect fruit quality. A few hardy hybrids can withstand temperatures well below freezing, but do not produce quality fruit. Lemons can be commercially grown in cooler-summer/moderate-winter, coastal Southern California, because sweetness is neither attained nor expected in retail lemon fruit. The related trifoliate orange (C. trifoliata) can survive below −20 °C (−4 °F); its fruit are astringent and inedible unless cooked, but a few better-tasting cultivars and hybrids have been developed (see citranges).

Leaf of Citrus tree Citrus leaf.JPG
Leaf of Citrus tree

The trees thrive in a consistently sunny, humid environment with fertile soil and adequate rainfall or irrigation. Abandoned trees in valleys may suffer, yet survive, the dry summer of Central California's Inner Coast Ranges. At any age, citrus grows well enough with infrequent irrigation in partial shade, but the fruit crop is smaller. Being of tropical and subtropical origin, oranges, like all citrus, are broadleaved and evergreen. They do not drop leaves except when stressed. The stems of many varieties have large sharp thorns. The trees flower in the spring, and fruit is set shortly afterward. Fruit begins to ripen in fall or early winter, depending on cultivar, and develops increasing sweetness afterward. Some cultivars of tangerines ripen by winter. Some, such as the grapefruit, may take up to 18 months to ripen.

Production

Major producer regions Hauptanbaugebiete-Zitrusfruchte.svg
Major producer regions

According to UN 2007 data, Brazil, China, the United States, Mexico, India, and Spain are the world's largest citrus-producing countries.

Major commercial citrus-growing areas include southern China, the Mediterranean Basin (including southern Spain), South Africa, Australia, the southern United States, Mexico, and parts of South America. In the United States, Florida, California, Arizona, and Texas are major producers, while smaller plantings are present in other Sun Belt states and in Hawaii.

As ornamental plants

Orangery of the Botanical Garden in Leuven (Belgium) Orangerie Kruidtuin Leuven.jpg
Orangery of the Botanical Garden in Leuven (Belgium)

Citrus trees grown in tubs and wintered under cover were a feature of Renaissance gardens, once glass-making technology enabled sufficient expanses of clear glass to be produced. An orangery was a feature of royal and aristocratic residences through the 17th and 18th centuries. The Orangerie at the Palace of the Louvre, 1617, inspired imitations that were not eclipsed until the development of the modern greenhouse in the 1840s. In the United States, the earliest surviving orangery is at the Tayloe House, Mount Airy, Virginia. George Washington had an orangery at Mount Vernon.

Some modern hobbyists still grow dwarf citrus in containers or greenhouses in areas where the weather is too cold to grow it outdoors. Consistent climate, sufficient sunlight, and proper watering are crucial if the trees are to thrive and produce fruit. Compared to many of the usual "green shrubs", citrus trees better tolerate poor container care. For cooler winter areas, limes and lemons should not be grown, since they are more sensitive to winter cold than other citrus fruits. Hybrids with kumquats (× Citrofortunella ) have good cold resistance. A citrus tree in a container may have to be repotted every 5 years or so, since the roots may form a thick "root-ball" on the bottom of the pot. [13]

Pests and diseases

Citrus canker is caused by the gammaproteobacterium Xanthomonas axonopodis Citrus canker on fruit.jpg
Citrus canker is caused by the gammaproteobacterium Xanthomonas axonopodis

Citrus plants are very liable to infestation by aphids, whitefly, and scale insects (e.g. California red scale). Also rather important are the viral infections to which some of these ectoparasites serve as vectors such as the aphid-transmitted Citrus tristeza virus , which when unchecked by proper methods of control is devastating to citrine plantations. The newest threat to citrus groves in the United States is the Asian citrus psyllid.

The Asian citrus psyllid is an aphid-like insect that feeds on the leaves and stems of citrus trees and other citrus-like plants. The real danger lies that the psyllid can carry a deadly, bacterial tree disease called Huanglongbing (HLB), also known as citrus greening disease. [36]

In August 2005, citrus greening disease was discovered in the south Florida region around Homestead and Florida City. The disease has since spread to every commercial citrus grove in Florida. In 2004–2005, USDA statistics reported the total Florida citrus production to be 169.1 million boxes of fruit. The estimate for all Florida citrus production in the 2015–2016 season is 94.2 million boxes, a 44.3% drop. [37]

In June 2008, the psyllid was spotted dangerously close to California – right across the international border in Tijuana, Mexico. Only a few months later, it was detected in San Diego and Imperial Counties, and has since spread to Riverside, San Bernardino, Orange, Los Angeles and Ventura Counties, sparking quarantines in those areas. The Asian citrus psyllid has also been intercepted coming into California in packages of fruit and plants, including citrus, ornamentals, herbs and bouquets of cut flowers, shipped from other states and countries. [36]

The foliage is also used as a food plant by the larvae of Lepidoptera (butterfly and moth) species such as the Geometridae common emerald (Hemithea aestivaria) and double-striped pug (Gymnoscelis rufifasciata), the Arctiidae giant leopard moth (Hypercompe scribonia), H. eridanus , H. icasia and H. indecisa , many species in the family Papilionidae (swallowtail butterflies), and the black-lyre leafroller moth ("Cnephasia" jactatana), a tortrix moth.

Since 2000, the citrus leafminer (Phyllocnistis citrella) has been a pest in California, [38] boring meandering patterns through leaves.

In eastern Australia, the bronze-orange bug ( Musgraveia sulciventris ) can be a major pest of citrus trees, particularly grapefruit. In heavy infestations it can cause flower and fruit drop and general tree stress.

European brown snails ( Cornu aspersum ) can be a problem in California, though laying female Khaki Campbell and other mallard-related ducks can be used for control.

Deficiency diseases

Citrus plants can also develop a deficiency condition called chlorosis, characterized by yellowing leaves [39] highlighted by contrasting leaf veins. The shriveling leaves eventually fall, and if the plant loses too many, it will slowly die. This condition is often caused by an excessively high pH (alkaline soil), which prevents the plant from absorbing iron, magnesium, zinc, or other nutrients it needs to produce chlorophyll. This condition can be cured by adding an appropriate acidic fertilizer formulated for citrus, which can sometimes revive a plant to produce new leaves and even flower buds within a few weeks under optimum conditions. A soil which is too acidic can also cause problems; citrus prefers neutral soil (pH between 6 and 8). Citrus plants are also sensitive to excessive salt in the soil. Soil testing may be necessary to properly diagnose nutrient-deficiency diseases. [40]

Uses

Culinary

Wedges of pink grapefruit, lime, and lemon, and a half orange (clockwise from top) NIH citrus.jpg
Wedges of pink grapefruit, lime, and lemon, and a half orange (clockwise from top)
Citrus aurantifolia in Kerala Citrus aurantiifolia in Kadavoor.jpg
Citrus aurantifolia in Kerala
Ripe Bitter oranges (Citrus x aurantium) from Asprovalta Pomeranzen.jpg
Ripe Bitter oranges (Citrus × aurantium) from Asprovalta

Many citrus fruits, such as oranges, tangerines, grapefruits, and clementines, are generally eaten fresh. They are typically peeled and can be easily split into segments. Grapefruit is more commonly halved and eaten out of the skin with a spoon. [41] Special spoons (grapefruit spoons) with serrated tips are designed for this purpose. Orange and grapefruit juices are also popular breakfast beverages. More acidic citrus, such as lemons and limes, are generally not eaten on their own. Meyer lemons can be eaten out of hand with the fragrant skin; they are both sweet and sour. Lemonade or limeade are popular beverages prepared by diluting the juices of these fruits and adding sugar. Lemons and limes are also used as garnishes or in cooked dishes. Their juice is used as an ingredient in a variety of dishes; it can commonly be found in salad dressings and squeezed over cooked fish, meat, or vegetables.

A variety of flavours can be derived from different parts and treatments of citrus fruits. The rind and oil of the fruit is generally very bitter, especially when cooked, so is often combined with sugar. The fruit pulp can vary from sweet to extremely sour. Marmalade, a condiment derived from cooked orange and lemon, can be especially bitter, but is usually sweetened to cut the bitterness and produce a jam-like result. Lemon or lime is commonly used as a garnish for water, soft drinks, or cocktails. Citrus juices, rinds, or slices are used in a variety of mixed drinks. The colourful outer skin of some citrus fruits, known as zest, is used as a flavouring in cooking; the white inner portion of the peel, the pith, is usually avoided due to its bitterness. The zest of a citrus fruit, typically lemon or an orange, can also be soaked in water in a coffee filter, and drunk.

Medical

Citrus fruits have well-documented nutritional and health benefits. [10] They can actually help prevent and cure some diseases. [10]

Citrus fruit intake has been associated with a 10% reduction in odds of developing breast cancer. [42]

Oranges were historically used for their high content of vitamin C, [29] which prevents scurvy. Scurvy is caused by vitamin C deficiency, and can be prevented by having 10 mg of vitamin C a day. An early sign of scurvy is fatigue. If ignored, later symptoms are bleeding and bruising easily. British sailors were given a ration of citrus fruits on long voyages to prevent the onset of scurvy, hence the British nickname of Limey.

Pectin is a structural heteropolysaccharide contained in the primary cell walls of plants. Limes and lemons, as well as oranges and grapefruits, are among the highest in this level. [43]

After consumption, the peel is sometimes used as a facial cleanser.

Before the development of fermentation-based processes, lemons were the primary commercial source of citric acid.

Citrus fruit intake is associated with a reduced risk of stomach cancer. [44] Lemons have the highest concentration of citrate of any citrus fruit, and daily consumption of lemonade has been shown to decrease the rate of kidney stone formation. [45]

Health effects

Some Citrus species contain significant amounts of furanocoumarins, a diverse family of naturally occurring organic chemical compounds. In humans, some (not all) of these chemical compounds act as strong photosensitizers when applied topically to the skin, while other furanocoumarins interact with medications when taken orally. The latter is called the “grapefruit juice effect”, a common name for a related group of grapefruit-drug interactions.

Due to the photosensitizing effects of certain furanocoumarins, some Citrus species are known to cause phytophotodermatitis, [46] a potentially severe skin inflammation resulting from contact with a light-sensitizing botanical agent followed by exposure to ultraviolet light. In Citrus species, the primary photosensitizing agent appears to be bergapten, [47] a linear furanocoumarin derived from psoralen. This claim has been confirmed for lime [48] [49] and bergamot. In particular, bergamot essential oil has a higher concentration of bergapten (3000–3600 mg/kg) than any other Citrus-based essential oil. [50]

In general, three Citrus ancestral species (pomelos, citrons, and papedas) synthesize relatively high quantities of furanocoumarins, whereas a fourth ancestral species (mandarins) is practically devoid of these compounds. [47] Since the production of furanocoumarins in plants is believed to be heritable, the descendants of mandarins (such as sweet oranges, tangerines, and other small mandarin hybrids) are expected to have low quantities of furanocoumarins, whereas other hybrids (such as limes, grapefruit, and sour oranges) are expected to have relatively high quantities of these compounds.

In one comprehensive study of 61 Citrus varieties, [47] two papedas ( Citrus micrantha and Citrus hystrix ) had the highest concentrations of furanocoumarins of any Citrus species (even more than the bergamot), in both the peel and the pulp. The study also found high furanocoumarin content in the peel of lime and bergamot, and in the pulp of pomelo, grapefruit, and sour orange. These results are consistent with what is already known, that is, lime and bergamot lead to phytophotodermatitis, while pomelo and grapefruit are involved in grapefruit-drug interactions.

In most Citrus species, the peel contains a greater diversity and a higher concentration of furanocoumarins than the pulp of the same fruit. [48] [49] [47] An exception is bergamottin, a furanocoumarin implicated in grapefruit-drug interactions, which is more concentrated in the pulp of certain varieties of pomelo, grapefruit, and sour orange.

List of citrus fruits

Citrons (Citrus medica) for sale in Germany Cedri BMK.jpg
Citrons (Citrus medica) for sale in Germany
Red Finger Lime (Citrus australasica), a rare delicacy from Australia Citrus australasica red whole.jpg
Red Finger Lime (Citrus australasica), a rare delicacy from Australia

The genus Citrus has been suggested to originate in the eastern Himalayan foothills. Prior to human cultivation, it consisted of just a few species, though the status of some as distinct species has yet to be confirmed:

Hybrids and cultivars

Sweetie or Oroblanco is a pomelo-grapefruit hybrid. Sweetie (Citrus).jpg
Sweetie or Oroblanco is a pomelo-grapefruit hybrid.
The etrog, or citron, is central to the ritual of the Jewish Sukkot festival. Many varieties are used for this purpose (including the Yemenite variety pictured). Yemenite.jpg
The etrog, or citron, is central to the ritual of the Jewish Sukkot festival. Many varieties are used for this purpose (including the Yemenite variety pictured).
Clementines (Citrus xclementina) have thinner skins than oranges. Clementinepeeled.jpg
Clementines (Citrus ×clementina) have thinner skins than oranges.
Mikan (Citrus xunshiu), also known as satsumas Citrus unshiu-unshu mikan-2.jpg
Mikan (Citrus ×unshiu), also known as satsumas
Sweet oranges (Citrus xsinensis) are used in many foods. Their ancestors were pomelos and mandarin oranges. Ambersweet oranges.jpg
Sweet oranges (Citrus ×sinensis) are used in many foods. Their ancestors were pomelos and mandarin oranges.
Cross-section of Odichukuthi lime Odichukuthi lime crossection.JPG
Cross-section of Odichukuthi lime
Odichukuthi fruit Odichukuthi naranga.JPG
Odichukuthi fruit
A pompia fruit Frutto pompia.jpg
A pompia fruit

Sorted by parentage. As each hybrid is the product of (at least) two parent species, they are listed multiple times.

Citrus maxima-based

Citrus medica-based

Citrus reticulata–based

Other/Unresolved

For hybrids with kumquats, see citrofortunella. For hybrids with the trifoliate orange, see citrange.

See also

Related Research Articles

Grapefruit citrus fruit

The grapefruit is a subtropical citrus tree known for its relatively large sour to semi-sweet, somewhat bitter fruit. Grapefruit is a citrus hybrid originating in Barbados as an accidental cross between two introduced species – sweet orange, and pomelo – both of which were introduced from Asia in the seventeenth century. When found, it was nicknamed the "forbidden fruit". Frequently, it is misidentified as the very similar parent species, pomelo.

Mandarin orange Species of plant

The mandarin orange, also known as the mandarin or mandarine, is a small citrus tree with fruit resembling other oranges, usually eaten plain or in fruit salads. Reddish-orange mandarin cultivars can be marketed as tangerines, but this is not a botanical classification.

Lime (fruit) citrus fruit

A lime is a citrus fruit, which is typically round, green in color, 3–6 centimetres (1.2–2.4 in) in diameter, and contains acidic juice vesicles.

Citron species of plant, citron

The citron is a large fragrant citrus fruit with a thick rind. It is one of the original citrus fruits from which all other citrus types developed through natural hybrid speciation or artificial hybridization. Though citron cultivars take on a wide variety of physical forms, they are all closely related genetically. It is used widely in Asian cuisine, and also in traditional medicines, perfume, and for religious rituals and offerings. Hybrids of citrons with other citrus are commercially prominent, notably lemons and many limes.

<i>Citrus limetta</i> species of plant

Citrus limetta, alternatively considered to be a cultivar of Citrus limon, C. limon 'Limetta', is a species of citrus, commonly known as mousambi, musambi, sweet lime, sweet lemon, and sweet limetta, it is a member of the sweet lemons. It is a cross between the citron and a bitter orange.

Tangelo nothospecies of plant, tangelo

The tangelo, Citrus × tangelo, is a citrus fruit hybrid of a Citrus reticulata variety such as mandarin orange or a tangerine, and Citrus maxima variety, such as a pomelo or grapefruit. The name is a portmanteau of ‘tangerine’ and ‘pomelo’.

Pomelo citrus fruit

The pomelo, Citrus maxima or Citrus grandis, is the largest citrus fruit from the Rutaceae family. It is a natural (non-hybrid) citrus fruit, similar in appearance to a large grapefruit, native to South and Southeast Asia. The pomelo is one of the original citrus species from which the rest of cultivated citrus have been hybridized. The popular fruit is used in many festive celebrations throughout Southeast Asia.

<i>Yuzu</i> citrus fruit and plant

Yuzu is a citrus fruit and plant in the family Rutaceae. It is called yuja in Korean cuisine. Both Japanese yuzu and Korean yuja are cognates of the Chinese yòuzi (柚子), but the Mandarin word refers to the pomelo. Yuzu is called xiāngchéng (香橙) in Mandarin.

Key lime species of plant, Key lime

The Key lime is a citrus hybrid with a spherical fruit, 2.5–5 cm (1–2 in) in diameter. The Key lime is usually picked while it is still green but it becomes yellow when ripe.

Rangpur (fruit) hybrid between the mandarin orange and the lemon

Rangpur, Citrus × limonia or Citrus reticulata x medica, sometimes called the rangpur lime, mandarin lime or lemandarin, is a hybrid between the mandarin orange and the citron.

Orange (fruit) citrus fruit

The orange is the fruit of the citrus species Citrus × sinensis in the family Rutaceae. It is also called sweet orange, to distinguish it from the related Citrus × aurantium, referred to as bitter orange. The sweet orange reproduces asexually ; varieties of sweet orange arise through mutations.

Sweet lemon Shoe Brand

Sweet lemon and sweet lime refer to many citrus hybrids that contain low acid pulp and juice. They are hybrids often similar to non-sweet lemons or limes, but with less citron parentage. Sweet limes and lemons are not sharply separated:

The sweet lime, Citrus limettioides Tan., is often confused with the sweet lemon, C. limetta Tan., which, in certain areas, is referred to as "sweet lime". In some of the literature, it is impossible to tell which fruit is under discussion.

Ponderosa lemon citrus species

The ponderosa lemon is a citrus hybrid of a pomelo and a citron. It is not the same as the 'Yuma Ponderosa' lemon pomello hybrid, that is used as citrus rootstock.

Papeda (citrus) subgenus of plants

Papeda or papaeda is the common name for a group of citrus native to tropical Asia that are hardy and slow growing, and produce unpalatable fruit. Walter Tennyson Swingle segregated these species into a separate subgenus, Papeda. It included the Ichang lemon, yuzu, kaffir lime, kabosu, sudachi, and a number of wild and uncultivated species and hybrids. Recent genetic analysis shows the papedas to be distributed among distinct branches of the citrus phylogenetic tree, and hence Swingle's proposed subgenus is polyphyletic and not a valid taxonomic grouping, but the term persists as a common name.

Cam sành cultivar of citrus fruit

The cam sành or King orange is a citrus hybrid originating in Vietnam.

Lemon citrus fruit

The lemon, Citrus limon (L.) Osbeck, is a species of small evergreen tree in the flowering plant family Rutaceae, native to South Asia, primarily North eastern India.

Shangjuan citrus fruit and plant originating in East Asia

The shangjuan, or Ichang lemon, is a cold-hardy citrus fruit and plant originating in East Asia.

Citrofortunella genus of plants

Citrofortunella are a large group of commercial hybrids that cross the kumquat with other citrus. In the system of citrus taxonomy established by Swingle, kumquats were placed in a different genus, Fortunella, from Citrus, which included citron, mandarin orange, pomelo and papedas. Such hybrids would then represent intergeneric hybrids, and a novel genus name was coined for them in 1975, by making a portmanteau of the names of the contributing genera to form Citrofortunella. That the genus is of a hybrid nature is indicated by a multiplication sign before the genus name, for example × Citrofortunella microcarpa. Recent phylogenetic work has shown kumquats to fall within Citrus rather than representing a distinct genus, meaning these would no longer represent intergeneric hybrids, and use of Citrofortunella as a distinct genus name for these hybrids loses taxonomic validity. They would instead fall within Citrus.

Rhobs el Arsa

Rhobs al-Arsa is a very popular citrus fruit in Morocco.

Citrus taxonomy Botanical classification of the genus Citrus

Citrus taxonomy refers to the botanical classification of the species, varieties, cultivars, and graft hybrids within the genus Citrus and related genera, found in cultivation and in the wild.

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Further reading