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''Citrus'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of flowering trees and
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from tree ...
s in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons,
grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit ...
s, pomelos, and limes. The genus ''Citrus'' is native to
South Asia South Asia is the southern subregion of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.;;;;; ...
,
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea ...
,
Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia, South-eastern Asia or SEA, is the geographical south-eastern region of Asia, consisting of the regions that are situated south of mainland ...
,
Melanesia Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from Indonesia's New Guinea in the west to Fiji in the east, and includes the Arafura Sea. The region includes the four independent countries of Fiji, V ...
, and
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
. Various citrus species have been used and domesticated by indigenous cultures in these areas since ancient times. From there its cultivation spread into
Micronesia Micronesia (, ) is a subregion of Oceania, consisting of about 2,000 small islands in the western Pacific Ocean. It has a close shared cultural history with three other island regions: the Philippines to the west, Polynesia to the east, ...
and
Polynesia Polynesia () "many" and νῆσος () "island"), to, Polinisia; mi, Porinihia; haw, Polenekia; fj, Polinisia; sm, Polenisia; rar, Porinetia; ty, Pōrīnetia; tvl, Polenisia; tkl, Polenihia (, ) is a subregion of Oceania, made up of ...
by the
Austronesian expansion The Austronesian peoples, sometimes referred to as Austronesian-speaking peoples, are a large group of peoples in Taiwan, Maritime Southeast Asia, Micronesia, coastal New Guinea, Island Melanesia, Polynesia, and Madagascar that speak Au ...
(c. 3000–1500 BCE); and to the Middle East and the
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on ...
(c. 1200 BCE) via the
incense trade route The Incense Trade Route was an ancient network of major land and sea trading routes linking the Mediterranean world with eastern and southern sources of incense, spices and other luxury goods, stretching from Mediterranean ports across the Le ...
, and onwards to Europe and the Americas.


History

Citrus plants are native to subtropical and tropical regions of Asia,
Island Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia or Oceanic Sout ...
, Near Oceania, and northeastern Australia. Domestication of citrus species involved much hybridization and
introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Intr ...
, leaving much uncertainty about when and where domestication first happened. A genomic, phylogenic, and biogeographical analysis by Wu ''et al.'' (2018) has shown that the center of origin of the genus ''Citrus'' is likely the southeast foothills of the
Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...
, in a region stretching from eastern
Assam Assam (; ) is a state in northeastern India, south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur ...
, northern
Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...
, to western
Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...
. It diverged from a common ancestor with ''
Poncirus trifoliata The trifoliate orange, ''Citrus trifoliata'' or ''Poncirus trifoliata'', is a member of the family Rutaceae. Whether the trifoliate oranges should be considered to belong to their own genus, ''Poncirus'', or be included in the genus ''Citrus'' i ...
''. A change in climate conditions during the
Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene Epoch made up of two stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million years ago) to 5.333 Ma. The ...
(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 Mainland Southeast Asia, also known as the Indochinese Peninsula or Indochina, is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to the west an ...
; the mandarins (''C. reticulata''), kumquats (''C. japonica''), mangshanyegan (''C. mangshanensis''), and ichang papedas (''C. cavaleriei'') of southeastern China; the kaffir limes (''C. hystrix'') of
Island Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia or Oceanic Sout ...
; and the biasong and samuyao (''C. micrantha'') of the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
. This was later followed by the spread of citrus species into
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia, at the junction of the East and South China Seas in the northwestern Pacific Ocean, with the People's Republic of China (PRC) to the northwest, Japan to the no ...
and Japan in the
Early Pliocene Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * ...
(5.33 to 3.6 mya), resulting in the tachibana orange (''C. tachibana''); and beyond the Wallace Line into
Papua New Guinea Papua New Guinea (abbreviated PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country i ...
and Australia during the
Early Pleistocene The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...
(2.5 million to 800,000 years ago), where further speciation events occurred resulting in the Australian limes. The earliest introductions of citrus species by human migrations was during the
Austronesian expansion The Austronesian peoples, sometimes referred to as Austronesian-speaking peoples, are a large group of peoples in Taiwan, Maritime Southeast Asia, Micronesia, coastal New Guinea, Island Melanesia, Polynesia, and Madagascar that speak Au ...
(c. 3000–1500 BCE), where '' Citrus hystrix'', '' Citrus macroptera'', and '' Citrus maxima'' were among the canoe plants carried by Austronesian voyagers eastwards into
Micronesia Micronesia (, ) is a subregion of Oceania, consisting of about 2,000 small islands in the western Pacific Ocean. It has a close shared cultural history with three other island regions: the Philippines to the west, Polynesia to the east, ...
and
Polynesia Polynesia () "many" and νῆσος () "island"), to, Polinisia; mi, Porinihia; haw, Polenekia; fj, Polinisia; sm, Polenisia; rar, Porinetia; ty, Pōrīnetia; tvl, Polenisia; tkl, Polenihia (, ) is a subregion of Oceania, made up of ...
. 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 Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...
, the
Levant The Levant () is an approximate historical geographical term referring to a large area in the Eastern Mediterranean region of Western Asia. In its narrowest sense, which is in use today in archaeology and other cultural contexts, it is ...
and the Mediterranean islands; and a maritime route through the
Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plat ...
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 Cyprus ; tr, Kıbrıs (), officially the Republic of Cyprus,, , lit: Republic of Cyprus is an island country located south of the Anatolian Peninsula in the eastern Mediterranean Sea. Its continental position is disputed; while it is ...
, dated to around 1200 BCE. Other archaeobotanical evidence include pollen from
Carthage Carthage was the capital city of Ancient Carthage, on the eastern side of the Lake of Tunis in what is now Tunisia. Carthage was one of the most important trading hubs of the Ancient Mediterranean and one of the most affluent cities of the classi ...
dating back to the 4th century BCE; and carbonized seeds from
Pompeii Pompeii (, ) was an ancient city located in what is now the ''comune'' of Pompei near Naples in the Campania region of Italy. Pompeii, along with Herculaneum and many villas in the surrounding area (e.g. at Boscoreale, Stabiae), was burie ...
dated to around the 3rd to 2nd century BCE. The earliest complete description of the citron was first attested from
Theophrastus Theophrastus (; grc-gre, Θεόφραστος ; c. 371c. 287 BC), a Greek philosopher and the successor to Aristotle in the Peripatetic school. He was a native of Eresos in Lesbos.Gavin Hardy and Laurence Totelin, ''Ancient Botany'', Routle ...
, c. 310 BCE. The agronomists of
classical Rome In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 BC ...
made many references to the cultivation of citrus fruits within the limits of their empire. Lemons, pomelos, and sour oranges are believed to have been introduced to the Mediterranean later by Arab traders at around the 10th century CE; and sweet oranges by the Genoese and Portuguese from Asia during the 15th to 16th century. Mandarins were not introduced until the 19th century. 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. Oranges were introduced to Florida by Spanish colonists. In cooler parts of Europe, citrus fruit was grown in orangeries starting in the 17th century; many were as much status symbols as functional agricultural structures.


Etymology

The generic name originated from
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
, where it referred to either the plant now known as citron (''C. medica'') or a conifer tree ('' Thuja''). It is related to the
ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...
word for cedar, κέδρος (''kédros''). This may be due to perceived similarities in the smell of citrus leaves and fruit with that of cedar. 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 species began to diverge from a common ancestor about 15 million years ago, at about the same time that '' Severinia'' (such as the
Chinese box orange ''Atalantia buxifolia'', synonym ''Severinia buxifolia'', is a species of plant in the family Rutaceae, related to ''Citrus'' and '' Citropsis''. Its common names include Chinese box-orange, box orange or boxthorn. It is native to southern China. I ...
) diverged from the same ancestor. About 7 million years ago, the ancestors of ''Citrus'' split into the main genus, ''Citrus'', and the genus ''Poncirus'' (such as the trifoliate orange), which is closely enough related that it can still be hybridized with all other citrus and used as rootstock. These estimates are made using genetic mapping of plant
chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it i ...
s. A DNA study published in ''
Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...
'' in 2018 concludes that the genus ''Citrus'' first evolved in the foothills of the
Himalaya The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 10 ...
s, in the area of
Assam Assam (; ) is a state in northeastern India, south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur ...
(India), western
Yunnan Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...
(China), and northern
Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...
. 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.


Fossil record

A
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
leaf from the
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Valdarno The Valdarno is the valley of the river Arno, although this name does not apply to the entire river basin. Usage of the term generally excludes Casentino and the valleys formed by major tributaries. Some towns in the area: *Rignano sull'Arno *Fi ...
(Italy) is described as †''Citrus meletensis''. 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 (6 miles) northwest of
Lincang City Lincang () is a prefecture-level city located in the southwest of Yunnan province, People's Republic of China. History Lincang was previously called Baihuai during the Shang dynasty. On December 26, 2003, the state council approved the cancell ...
, Yunnan. The Bangmai Formation contains abundant fossil plants and is considered to be of late
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
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.


Taxonomy

The
taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
and
systematics Biological systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: cladograms, phylogenetic t ...
of the genus are complex and the precise number of natural
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
is unclear, as many of the named species are hybrids clonally propagated through seeds (by
apomixis In botany, apomixis is asexual reproduction without fertilization. Its etymology is Greek for "away from" + "mixing". This definition notably does not mention meiosis. Thus "normal asexual reproduction" of plants, such as propagation from cuttin ...
), and genetic evidence indicates that even some wild, true-breeding species are of hybrid origin. Most cultivated ''Citrus'' spp. seem to be
natural Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans ar ...
or artificial hybrids of a small number of core ancestral species, including the citron, pomelo, mandarin, and papeda (see image). Natural and cultivated
citrus hybrid 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. Citrus taxonomy is complex and controversial. ...
s include commercially important fruit such as oranges,
grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit ...
, lemons, limes, and some
tangerine The tangerine is a type of citrus fruit that is orange in color. Its scientific name varies. It has been treated as a separate species under the name ''Citrus tangerina'' or ''Citrus'' × ''tangerina'', or treated as a variety of '' Citrus reti ...
s. 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''. Trifoliate orange, which is often used as commercial rootstock, is an outgroup and may or may not be categorized as a citrus.
Phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...
analysis suggested the species of '' Oxanthera'' from
New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...
, commonly known as false oranges, should be transferred to the genus ''Citrus''.Bayer, R. J., et al. (2009)
A molecular phylogeny of the orange subfamily (Rutaceae: Aurantioideae) using nine cpDNA sequences.
''American Journal of Botany'' 96(3), 668–85.
The transfer has been accepted.


Description


Tree

These plants are large shrubs or small to moderate-sized trees, reaching tall, with spiny shoots and alternately arranged
evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, whic ...
leaves A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...
with an entire margin. The
flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanis ...
s are solitary or in small corymbs, each flower diameter, with five (rarely four) white petals and numerous stamens; they are often very strongly scented, due to the presence of essential oil glands.


Fruit

The fruit is a hesperidium, a specialised berry, globose to elongated, long and 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 A locule (plural locules) or loculus (plural loculi) (meaning "little place" in Latin) is a small cavity or compartment within an organ or part of an organism (animal, plant, or fungus). In angiosperms (flowering plants), the term ''locule'' usu ...
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. Many citrus
cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture ...
s have been developed to be seedless (see
nucellar embryony Nucellar embryony (notated Nu+) is a form of seed reproduction that occurs in certain plant species, including many citrus varieties. Nucellar embryony is a type of apomixis, where eventually nucellar embryos from the nucellus tissue of the ovule ...
and
parthenocarpy In botany and horticulture, parthenocarpy is the natural or artificially induced production of fruit without fertilisation of ovules, which makes the fruit seedless. Stenospermocarpy may also produce apparently seedless fruit, but the seeds ar ...
) and easy to peel. Citrus fruits are notable for their fragrance, partly due to
flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...
s and limonoids (which in turn are
terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ...
s) contained in the rind, and most are juice-laden. The juice contains a high quantity of
citric acid Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in ...
and other organic acids 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 Vitamin C (also known as ascorbic acid and ascorbate) is a water-soluble vitamin found in citrus and other fruits and vegetables, also sold as a dietary supplement and as a topical 'serum' ingredient to treat melasma (dark pigment spots) ...
. The content of vitamin C in the fruit depends on the species, variety, and mode of cultivation. The flavonoids include various
flavanone The flavanones, a type of flavonoids, are various aromatic, colorless ketones derived from flavone that often occur in plants as glycosides. List of flavanones * Blumeatin * Butin * Eriodictyol * Hesperetin * Hesperidin * Homoeriodictyol * ...
s and flavones.


Cultivation

Citrus trees hybridise very readily – depending on the
pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...
source, plants grown from a
Persian lime Persian lime (''Citrus'' × ''latifolia''), also known by other common names such as seedless lime, Bearss lime and Tahiti lime, is a citrus fruit species of hybrid origin, known only in cultivation. The Persian lime is a triploid cross between ...
's seeds can produce fruit similar to grapefruit. Thus, all commercial citrus cultivation uses trees produced by
grafting Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion () while the lower part is called the rootstock. The succ ...
the desired fruiting
cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture ...
s onto rootstocks selected for disease resistance and hardiness. The colour of citrus fruits only develops in climates with a ( diurnal) cool winter. In tropical regions with no winter at all, citrus fruits remain green until maturity, hence the tropical "green oranges". 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. 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, softening, and change in the fruit's colour. Citrus fruits are non climacteric and respiration slowly declines and the production and release of ethylene is gradual. 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 they are ready to eat. Citrus trees are not generally
frost Frost is a thin layer of ice on a solid surface, which forms from water vapor in an above-freezing atmosphere coming in contact with a solid surface whose temperature is below freezing, and resulting in a phase change from water vapor (a g ...
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 , but realistically temperatures not falling below are required for successful cultivation. Tangerines, tangors and
yuzu Yuzu (''Citrus junos'', from Japanese or ) is a citrus fruit and plant in the family Rutaceae of East Asian origin. Yuzu has been cultivated mainly in East Asia, though recently also in New Zealand, Australia, Spain, Italy, and France. ...
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 ; its fruit are astringent and inedible unless cooked, but a few better-tasting cultivars and hybrids have been developed (see citranges). 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 The Inner Coast Ranges are a long mountain range subsystem of the California Coast Ranges, running generally north–south in western California, from Santa Barbara County north to the Klamath Mountains system. Geography The term ''inner'' is a re ...
. 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

According to the UN Food and Agriculture Organization, world production of all citrus fruits in 2016 was , with about half of this production as oranges. At US $15.2 billion equivalent in 2018, citrus trade makes up nearly half of the world fruit trade, which was US $32.1 billion for the same year. According to the
United Nations Conference on Trade and Development The United Nations Conference on Trade and Development (UNCTAD) is an intergovernmental organization within the United Nations Secretariat that promotes the interests of developing countries in world trade. It was established in 1964 by the ...
(UNCTAD), citrus production grew during the early 21st century mainly by the increase in cultivation areas, improvements in transportation and packaging, rising incomes and consumer
preference In psychology, economics and philosophy, preference is a technical term usually used in relation to choosing between alternatives. For example, someone prefers A over B if they would rather choose A than B. Preferences are central to decision th ...
for healthy foods. In 2019–20, world production of oranges was estimated to be , led by Brazil, Mexico, the European Union, and China as the largest producers.


As ornamental plants

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 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 ...
'') 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.


Pests and diseases

Citrus plants are very liable to infestation by aphids, whitefly, and
scale insect Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than th ...
s (e.g. California red scale). Also rather important are the viral infections to which some of these
ectoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
s serve as vectors such as the aphid-transmitted ''
Citrus tristeza virus Citrus tristeza virus (CTV) is a viral species of the genus ''Closterovirus'' that causes the most economically damaging disease to its namesake plant genus, ''Citrus''. The disease has led to the death of millions of ''Citrus'' trees all over ...
'', 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 ''Diaphorina citri'', the Asian citrus psyllid, is a sap-sucking, hemipteran bug in the family Psyllidae. It is one of two confirmed vectors of citrus greening disease. It has a wide distribution in southern Asia and has spread to other citrus ...
. 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 in the fact that the psyllid can carry a deadly, bacterial tree disease called Huanglongbing (HLB), also known as citrus greening disease. Because the causative bacteria are not culturable, evaluation of resistant
cultivars A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
and vectors is slow. There are some HLB-resistant and vector-resistant citrus strains known, and
genetic engineering Genetic engineering, also called genetic modification or genetic manipulation, is the modification and manipulation of an organism's genes using technology. It is a set of technologies used to change the genetic makeup of cells, including ...
and new chemical controls have been proven in laboratory use and show promise for field use. 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. Carolyn Slupsky, a professor of nutrition and food science at the
University of California, Davis The University of California, Davis (UC Davis, UCD, or Davis) is a public land-grant research university near Davis, California. Named a Public Ivy, it is the northernmost of the ten campuses of the University of California system. The inst ...
has said that "we could lose all fresh citrus within 10 to 15 years". In June 2008, the psyllid was spotted dangerously close to California – right across the international border in
Tijuana Tijuana ( ,"Tijuana"
(US) and
< ...
, 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. The foliage is also used as a food plant by the
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...
e of
Lepidoptera Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described speci ...
(
butterfly Butterflies are insects in the macrolepidopteran clade Rhopalocera from the order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The group compris ...
and
moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...
) species such as the Geometridae
common emerald The common emerald (''Hemithea aestivaria'') is a moth of the family Geometridae. The species is found throughout the Nearctic and Palearctic regions and the Near East. It is mostly commonly found in the southern half of the British Isles. It was ...
(''Hemithea aestivaria'') and
double-striped pug The double-striped pug (''Gymnoscelis rufifasciata'') is a moth of the family Geometridae. It is a widespread and common species, being found throughout the Palearctic region, including the Near East and North Africa. This is a variable speci ...
(''Gymnoscelis rufifasciata''), the
Arctiidae The Arctiinae (formerly called the family Arctiidae) are a large and diverse subfamily of moths with around 11,000 species found all over the world, including 6,000 neotropical species.Scoble, MJ. (1995). ''The Lepidoptera: Form, Function and ...
giant leopard moth The giant leopard moth (''Hypercompe scribonia'') is a moth of the family Erebidae. They are distributed through North America from southern Ontario, and southern and eastern United States through New England, Mexico and south to Colombia. The ...
(''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 The citrus leafminer (''Phyllocnistis citrella'') is a moth of the family Gracillariidae. It is also known as CLM in agriculture. It was first found in Florida in 1993, but is now found all over the world, including Argentina, Australia, Brazi ...
(''Phyllocnistis citrella'') has been a pest in California, 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 The Campbell is a British breed of domestic duck. It was developed at Uley, in Gloucestershire, England, at the turn of the 20th century; being introduced to the public in 1898 and the Khaki variety in 1901. History Mrs Adele Campbell GRO & ...
and other
mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Argen ...
-related ducks can be used for control.


Deficiency diseases

Citrus plants can also develop a deficiency condition called chlorosis, characterized by yellowing leavesOnline at SumoGardener 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 Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
,
zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
, or other nutrients it needs to produce
chlorophyll Chlorophyll (also chlorophyl) is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words , ("pale green") and , ("leaf"). Chlorophyll allow plants to ...
. 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 Soil test may refer to one or more of a wide variety of soil analysis conducted for one of several possible reasons. Possibly the most widely conducted soil tests are those done to estimate the plant-available concentrations of plant nutrients, i ...
may be necessary to properly diagnose nutrient-deficiency diseases.


Uses


Culinary

Many citrus fruits, such as oranges,
tangerine The tangerine is a type of citrus fruit that is orange in color. Its scientific name varies. It has been treated as a separate species under the name ''Citrus tangerina'' or ''Citrus'' × ''tangerina'', or treated as a variety of '' Citrus reti ...
s,
grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit ...
s, 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. 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 Lemonade is a sweetened lemon-flavored beverage. There are varieties of lemonade found throughout the world. In North America and South Asia, cloudy still lemonade is the most common variety. There it is traditionally a homemade drink using ...
or limeade are popular beverages prepared by diluting the juices of these fruits and adding sugar. Lemons and limes are also used in cooked dishes, or sliced and used as garnishes. 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 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 with sugar 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. File:NIH citrus.jpg, Wedges of pink
grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit ...
, lime, and lemon, and a half orange (clockwise from top) File:Calamansi (sliced) - Philippines.jpg, Calamansi, a ubiquitous part of traditional dipping sauces and condiments in Philippine cuisine File:Citrus aurantiifolia in Kadavoor.jpg, '' Citrus aurantifolia'' in
Kerala Kerala ( ; ) is a state on the Malabar Coast of India. It was formed on 1 November 1956, following the passage of the States Reorganisation Act, by combining Malayalam-speaking regions of the erstwhile regions of Cochin, Malabar, South Ca ...
File:Pomeranzen.jpg, Ripe bitter oranges (''Citrus × aurantium'') from Asprovalta


Phytochemicals and research

Some ''Citrus'' species contain significant amounts of the
phytochemical Phytochemicals are chemical compounds produced by plants, generally to help them resist fungi, bacteria and plant virus infections, and also consumption by insects and other animals. The name comes . Some phytochemicals have been used as poison ...
class called
furanocoumarin The furanocoumarins, or furocoumarins, are a class of organic chemical compounds produced by a variety of plants. Most of the plant species found to contain furanocoumarins belong to a handful of plant families. The families Apiaceae and Rutace ...
s, 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, a potentially severe skin inflammation resulting from contact with a light-sensitizing botanical agent followed by exposure to
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
light. In ''Citrus'' species, the primary photosensitizing agent appears to be
bergapten Bergapten (5-methoxypsoralen) is a naturally-occurring organic chemical compound produced by numerous plant species, especially from the carrot family Apiaceae and the citrus family Rutaceae. For example, bergapten has been extracted from 24  ...
, a linear furanocoumarin derived from psoralen. This claim has been confirmed for lime and bergamot. In particular, bergamot essential oil has a higher concentration of bergapten (3000–3600 mg/kg) than any other ''Citrus''-based essential oil. 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. 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 most ''Citrus'' species, the peel contains a greater diversity and a higher concentration of furanocoumarins than the pulp of the same fruit. An exception is
bergamottin Bergamottin (5-geranoxypsoralen) is a natural furanocoumarin found in the pulp of pomelos and grapefruits. It is also found in the peel and pulp of the bergamot orange, from which it was first isolated and from which its name is derived. Chemis ...
, a furanocoumarin implicated in grapefruit-drug interactions, which is more concentrated in the pulp of certain varieties of pomelo, grapefruit, and sour orange. One review of preliminary research on diets indicated that consuming citrus fruits was associated with a 10% reduction of risk for developing breast cancer.


List of citrus fruits

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: * '' Citrus assamensis'' – ginger lime, from
Assam Assam (; ) is a state in northeastern India, south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur ...
and Bangladesh * '' Citrus crenatifolia'' – species name is unresolved, from
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
* ''
Citrus japonica Kumquats (; zh, 金桔), or cumquats in Australian English, are a group of small fruit-bearing trees in the flowering plant family Rutaceae. Their taxonomy is disputed. They were previously classified as forming the now-historical genus ''Fortun ...
'' – kumquats, from East Asia ranging into Southeast Asia (sometimes separated into four-five ''Fortunella'' species) * ''
Citrus mangshanensis ''Citrus mangshanensis'', the mangshanyegan (), is a wild citrus fruit species. The mangshanyegan is native to mountain forests in Mangshan, Hunan province, China, where it was first reported in the 1980s. It is genetically distinct from the ...
'' – species name is unresolved, from
Hunan Hunan (, ; ) is a landlocked province of the People's Republic of China, part of the South Central China region. Located in the middle reaches of the Yangtze watershed, it borders the province-level divisions of Hubei to the north, Jiangx ...
, China * '' Citrus maxima'' – pomelo (pummelo, shaddock), from the
Island Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia or Oceanic Sout ...
* '' Citrus medica'' – citron, from India * '' Citrus platymamma'' – ''byeonggyul'', from Jeju Island,
Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic ...
* '' Citrus reticulata'' – mandarin orange, from China * ''
Citrus trifoliata The trifoliate orange, ''Citrus trifoliata'' or ''Poncirus trifoliata'', is a member of the family Rutaceae. Whether the trifoliate oranges should be considered to belong to their own genus, ''Poncirus'', or be included in the genus ''Citrus'' is ...
'' – trifoliate orange, from Korea and adjacent China (often separated as ''Poncirus'') * Australian limes **'' Citrus australasica'' – Australian finger lime ** '' Citrus australis'' – Australian round lime ** '' Citrus garrawayi '' – Mount White lime ** '' Citrus glauca'' – Australian desert lime ** '' Citrus gracilis'' – Kakadu lime or Humpty Doo lime ** '' Citrus inodora'' – Russel River lime and Maiden's Australian lime ** '' Citrus warburgiana '' – New Guinea wild lime ** '' Citrus wintersii '' – Brown River finger lime * Papedas, including **'' Citrus halimii'' – ''limau kadangsa'', ''limau kedut kera'', from
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
and Malaya ** '' Citrus hystrix'' – Kaffir lime, ''makrut'', from
Mainland Southeast Asia Mainland Southeast Asia, also known as the Indochinese Peninsula or Indochina, is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of Mainland China and is bordered by the Indian Ocean to the west an ...
to
Island Southeast Asia Maritime Southeast Asia comprises the countries of Brunei, Indonesia, Malaysia, the Philippines, Singapore, and East Timor. Maritime Southeast Asia is sometimes also referred to as Island Southeast Asia, Insular Southeast Asia or Oceanic Sout ...
** '' Citrus cavaleriei'' – Ichang papeda from southern China ** '' Citrus celebica'' – Celebes papeda ** '' Citrus indica'' – Indian wild orange, from the
Indian subcontinent The Indian subcontinent is a physiographical region in Southern Asia. It is situated on the Indian Plate, projecting southwards into the Indian Ocean from the Himalayas. Geopolitically, it includes the countries of Bangladesh, Bhutan, In ...
** '' Citrus latipes'' – Khasi papeda, from
Assam Assam (; ) is a state in northeastern India, south of the eastern Himalayas along the Brahmaputra and Barak River valleys. Assam covers an area of . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Manipur ...
, Meghalaya, Burma ** '' Citrus longispina'' – Megacarpa papeda, winged lime, blacktwig lime ** '' Citrus macrophylla'' – Alemow ** '' Citrus macroptera'' – Melanesian papeda from Indochina to Melanesia ** ''
Citrus micrantha The micrantha is a wild citrus from the papeda group, native to southern Philippines, particularly islands of Cebu and Bohol. Two varieties are recognized: small-flowered papeda (''C. hystrix'' var. ''micrantha''), locally known as ''biaso ...
, Citrus westeri'' – ''biasong'' or ''samuyao'' from the southern Philippines ** '' Citrus webberi'' – Kalpi, Malayan lemon


Hybrids and cultivars

Sorted by parentage. As each hybrid is the product of (at least) two parent species, they are listed multiple times. ''Citrus maxima''-based * Amanatsu, natsumikan – ''Citrus'' ×''natsudaidai'' (''C. maxima'' × unknown) * Cam sành – (''C. reticulata'' × ''C.'' ×''sinensis'') * Dangyuja – (''Citrus grandis Osbeck'') *
Grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit ...
– ''Citrus'' ×''paradisi'' (''C. maxima'' × ''C.'' ×''sinensis'') * Haruka – ''Citrus tamurana'' x ''natsudaidai'' *
Hassaku orange Hassaku orange ( ja, 八朔, also called "jagada",) is Japanese citrus hybrid (biology), hybrid similar to an orange (fruit), orange in color but with the size of a grapefruit. The original plant was discovered near the Jōdo Temple in Inno-shi ...
– (''Citrus hassaku'') * Ichang lemon – (''Citrus wilsonii'') *
Imperial lemon The Imperial lemon is thought to be a lemon and grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented a ...
– (''C.'' ×''limon'' × ''C.'' ×''paradisi'') *
Kawachi Bankan Kawachi Bankan (''Citrus kawachiensis''), also called Mishokan and Uwa Gold, is a ''Citrus'' hybrid cultivated for its edible fruit. Genetics Two varieties of Kawachi Bankan have been identified: one, a hybrid between the ujukitsu (seed paren ...
– (''Citrus kawachiensis'') * Kinnow – (''C.'' ×''nobilis'' × ''C.'' ×''deliciosa'') * Kiyomi – (''C.'' ×''sinensis'' × ''C.'' ×''unshiu'') *
Minneola tangelo The tangelo ( , ; ''C. reticulata × C. maxima'' or ''× C. paradisi''), ''Citrus × tangelo, is'' a citrus fruit hybrid of a ''Citrus reticulata'' variety, such as mandarin orange or tangerine, and a ''Citrus maxima'' variety, such as a pome ...
– (''C. reticulata'' × ''C.'' ×''paradisi'') *
Orangelo An orangelo (Spanish ''chironja'' – ''C. paradisi'' × ''C. sinensis'') is a hybrid citrus fruit believed to have originated in Puerto Rico. The fruit, a cross between a grapefruit and an orange, had spontaneously appeared in the shade-providi ...
, Chironja – (''C.'' ×''paradisi'' × ''C.'' ×''sinensis'') *
Oroblanco An oroblanco, oro blanco (white gold), Pomelit (Israel) or sweetie (''Citrus grandis'' Osbeck × '' C. Paradisi'' Macf.) is a sweet seedless citrus hybrid fruit similar to grapefruit. It is often referred to as oroblanco grapefruit. Development ...
, Sweetie – (''C. maxima'' × ''C.'' ×''paradisi'') * Sweet orange – ''Citrus'' ×''sinensis'' (probably ''C. maxima'' × ''C. reticulata'') *
Tangelo The tangelo ( , ; ''C. reticulata × C. maxima'' or ''× C. paradisi''), ''Citrus × tangelo, is'' a citrus fruit hybrid of a ''Citrus reticulata'' variety, such as mandarin orange or tangerine, and a ''Citrus maxima'' variety, such as a pome ...
– ''Citrus'' ×''tangelo'' (''C. reticulata'' × ''C. maxima'' or ''C.'' ×''paradisi'') * Tangor – ''Citrus'' ×''nobilis'' (''C. reticulata'' × ''C.'' ×''sinensis'') * Ugli – (''C. reticulata'' × ''C. maxima'' or ''C.'' ×''paradisi'') ''Citrus medica''-based * Alemow, Colo – ''Citrus'' ×''macrophylla'' (''C. medica'' × ''C. micrantha'') *
Buddha's hand ''Citrus medica'' var. ''sarcodactylis'', or the fingered citron, is an unusually-shaped citron variety whose fruit is segmented into finger-like sections, resembling those seen on representations of the Buddha. It is called Buddha's hand in m ...
– ''Citrus medica'' var. ''sarcodactylus'', a fingered citron. * Citron varieties with sour pulpDiamante citron, Florentine citron, Greek citron and
Balady citron The balady citron is a variety of citron, or ''etrog'', grown in Israel and Palestine, mostly for Jewish ritual purposes. Not native to the region, it was imported around 500 or 300 BCE by either Jewish or Greek settlers. Initially not widely gro ...
* Citron varieties with sweet pulp – Corsican citron and
Moroccan citron The Moroccan citron ( he, אֶתְרוֹג מָרוֹקָנִי) is a true citron variety native to Assads, Morocco, which is still today its main center of cultivation. Sweet citron The Moroccan citron was described by the Moroccan professo ...
. *
Etrog Etrog ( he, אֶתְרוֹג, plural: '; Ashkenazi Hebrew: ', plural: ') is the yellow citron or ''Citrus medica'' used by Jews during the week-long holiday of Sukkot as one of the four species. Together with the ''lulav'', ''hadass'', and '' a ...
, a group of citron cultivars that are traditionally used for a Jewish ritual. ''Etrog'' is
Hebrew Hebrew (; ; ) is a Northwest Semitic language of the Afroasiatic language family. Historically, it is one of the spoken languages of the Israelites and their longest-surviving descendants, the Jews and Samaritans. It was largely preserved ...
for citron in general. * Fernandina – ''Citrus'' ×''limonimedica'' (probably (''C. medica'' × ''C. maxima'') × ''C. medica'') * Ponderosa lemon – (probably (''C. medica'' × ''C. maxima'') × ''C. medica'') * Lemon – ''Citrus '' ×''limon'' (''C. medica'' × ''C.'' ×''aurantium'') * Key lime, Mexican lime, Omani lime – ''Citrus'' ×''aurantiifolia'' (''C. medica'' × ''C. micrantha'') *
Persian lime Persian lime (''Citrus'' × ''latifolia''), also known by other common names such as seedless lime, Bearss lime and Tahiti lime, is a citrus fruit species of hybrid origin, known only in cultivation. The Persian lime is a triploid cross between ...
, Tahiti lime – ''C.'' ×''latifolia'' (''C.'' ×''aurantiifolia'' × ''C.'' ×''limon'') * Limetta, Sweet Lemon, Sweet Lime, mosambi – ''Citrus'' ×''limetta'' (''C. medica'' × ''C.'' ×''aurantium'') * Lumia – several distinct pear shaped lemon-like hybrids * Pompia – ''Citrus medica tuberosa'' Risso & Poiteau, 1818 (''C. medica'' × ''C.'' ×''aurantium''), native to
Sardinia Sardinia ( ; it, Sardegna, label=Italian, Corsican and Tabarchino ; sc, Sardigna , sdc, Sardhigna; french: Sardaigne; sdn, Saldigna; ca, Sardenya, label= Algherese and Catalan) is the second-largest island in the Mediterranean Sea, aft ...
, genetically synonymous with Rhobs el Arsa. * Rhobs el Arsa – 'bread of the garden', ''C. medica'' × ''C.'' ×''aurantium'', from
Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to A ...
. *
Yemenite citron The Yemenite citron ( he, אֶתְרוֹג תֵּימָנִי, '' etrog teimani'') is a variety of citron, usually containing no juice vesicles in its fruit's segments. The bearing tree and the mature fruit's size are somewhat larger than the tre ...
– a pulpless true citron. ''Citrus reticulata''–based * Bergamot orange – ''Citrus'' ×''bergamia'' (''C.'' ×''limon'' × ''C.'' ×''aurantium'') * Bitter orange, Seville Orange – ''Citrus'' ×''aurantium'' (''C. maxima'' × ''C. reticulata'') * Blood orange – ''Citrus'' ×''sinensis''
cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture ...
s * Calamansi, Calamondin – (''Citrus reticulata'' × ''Citrus japonica'') * Cam sành – (''C. reticulata'' × ''C.'' ×''sinensis'') * Chinotto – ''Citrus'' ×''aurantium'' var. ''myrtifolia'' or ''Citrus'' ×''myrtifolia'' * ChungGyun – ''Citrus reticulata'' cultivar * Clementine – ''Citrus'' ×''clementina'' * Cleopatra Mandarin – ''Citrus'' ×''reshni'' * Siranui – ''Citrus reticulata'' cv. 'Dekopon' (ChungGyun × Ponkan) * Daidai – ''Citrus'' ×''aurantium'' var. ''daidai'' or ''Citrus'' ×''daidai'' *
Encore An encore is an additional performance given by performers after the planned show has ended, usually in response to extended applause from the audience.Lalange Cochrane, in ''Oxford Companion to Music'', Alison Latham, ed., Oxford University Pre ...
– ((''Citrus reticulata'' x ''sinensis'') x ''C. deliciosa'') *
Grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit ...
– ''Citrus'' ×''paradisi'' (''C. maxima'' × ''C.'' ×''sinensis'') * Hermandina – ''Citrus reticulata'' cv. 'Hermandina' *
Imperial lemon The Imperial lemon is thought to be a lemon and grapefruit The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented a ...
– ((''C. maxima'' × ''C. medica'') × ''C.'' ×''paradisi'') * Iyokan, ''anadomikan'' – ''Citrus'' ×''iyo'' * Jabara – (''Citrus jabara'') *
Kanpei Kanpei, also known as Ehime queen splash, is a ''Citrus'' cultivar that originated in Japan. Genetics Kanpei was created by crossing the dekopon and nishinokaori varieties in 1991, although it was not officially introduced until August 2007. De ...
– (''Citrus reticulata'' 'Kanpei') * Kinkoji unshiu – (''Citrus obovoidea'' x ''unshiu'') * Kinnow, Wilking – (''C.'' ×''nobilis'' × ''C.'' ×''deliciosa'') *
Kishumikan The kishu mikan (''Citrus kinokuni'' ex Tanaka) is a hybrid variety of mikan, or mandarin orange (''Citrus reticulata''), found in Southern China and also grown in Japan. It is not closely related to the common sweet orange, but it is closely ...
– (''Citrus kinokuni'') * Kiyomi – (''C. sinensis'' × ''C.'' ×''unshiu'') * Kobayashi mikan – (''Citrus natsudaidai'' x ''unshiu'') *
Koji orange Koji orange (''Citrus leiocarpa''), also called smooth-fruited orange in English, bingyul in Korean, 光橘 (Guang ju), 柑 子 (Gan zi), and 日本土柑 (Ri ben tu gan) in Chinese, and コウジ (Kōji) in Japanese, is a ''Citrus'' species nativ ...
– (''Citrus leiocarpa'') *
Kuchinotsu No.37 Kuchinotsu No. 37 is a tangor cultivar grown in Japan. Genetics Kuchinotsu No. 37 was created by crossing the "Kiyomi" tangor with the 'Encore' mandarin. Hybrids It is a parent of the setoka along with the " Murcott" tangor, and is a parent of ...
– (' Kiyomi' x 'Encore') * Laraha – 'C.'' ×''aurantium'' ssp. ''currassuviencis'' * Mediterranean mandarin, Willow Leaf – ''Citrus'' ×''deliciosa'' * Meyer lemon, Valley Lemon – ''Citrus'' ×''meyeri'' (''C. medica'' × ''C.'' ×''sinensis'') * Michal mandarin – ''Citrus reticulata'' cv. 'Michal' * Mikan, Satsuma – ''Citrus'' ×''unshiu'' * Murcott – (''C. reticulata'' x ''sinensis'') * Naartjie – (''C. reticulata'' × ''C. nobilis'') * Nova mandarin, Clemenvilla *
Orangelo An orangelo (Spanish ''chironja'' – ''C. paradisi'' × ''C. sinensis'') is a hybrid citrus fruit believed to have originated in Puerto Rico. The fruit, a cross between a grapefruit and an orange, had spontaneously appeared in the shade-providi ...
, Chironja – (''C.'' ×''paradisi'' × ''C.'' ×''sinensis'') *
Oroblanco An oroblanco, oro blanco (white gold), Pomelit (Israel) or sweetie (''Citrus grandis'' Osbeck × '' C. Paradisi'' Macf.) is a sweet seedless citrus hybrid fruit similar to grapefruit. It is often referred to as oroblanco grapefruit. Development ...
, Sweetie – (''C. maxima'' × ''C.'' ×''paradisi'') * – ''Citrus'' ×''limettioides'' Tanaka (''C. medica'' × ''C.'' ×''sinensis'') * Ponkan – ''Citrus reticulata'' cv. 'Ponkan' * Rangpur, Lemanderin, Mandarin Lime – ''Citrus'' ×''limonia'' (''C. reticulata'' × ''C. medica'') * Reikou – (Kuchinotsu No.37 x 'Murcott') *
Rough lemon Rough lemon (''Citrus'' × ''jambhiri'' Lush.) is the fruit and the tree of a citrus hybrid. Like the rangpur, it is a cross between mandarin orange and citron. Rough lemon is a cold-hardy citrus and can grow into a large tree. The rough lemon ...
– ''Citrus'' ×''jambhiri'' Lush. (''C. reticulata'' × ''C. medica'') *
Sanbokan Sanbokan (''Citrus sulcata'' Takahashi, :ja:さんぼうかん or 'Sanbokan', ) is a Japanese citrus fruit of the Wakayama prefecture similar to a mandarin orange, easily distinguished by its pronounced basal nipple. Parentage is unknown. Fruit ...
– ''Citrus sulcata'' * Setoka – (Kuchinotsu No.37 x 'Murcott') * Shekwasha, Hirami Lemon, Taiwan Tangerine – ''Citrus'' ×''depressa'' * Sunki, Suenkat – ''Citrus'' ''sunki'' or ''C. reticulata'' var. ''sunki'' * Sweet orange – ''Citrus'' ×''sinensis'' (''C. maxima'' × ''C. reticulata'') * Tachibana orange – ''Citrus'' ''tachibana'' (Mak.) Tanaka or ''C. reticulata'' var. ''tachibana'' *
Tangelo The tangelo ( , ; ''C. reticulata × C. maxima'' or ''× C. paradisi''), ''Citrus × tangelo, is'' a citrus fruit hybrid of a ''Citrus reticulata'' variety, such as mandarin orange or tangerine, and a ''Citrus maxima'' variety, such as a pome ...
– ''Citrus'' ×''tangelo'' (''C. reticulata'' × ''C. maxima'' or ''C.'' ×''paradisi'') *
Tangerine The tangerine is a type of citrus fruit that is orange in color. Its scientific name varies. It has been treated as a separate species under the name ''Citrus tangerina'' or ''Citrus'' × ''tangerina'', or treated as a variety of '' Citrus reti ...
– ''Citrus'' ×''tangerina'' * Tangor – ''Citrus'' ×''nobilis'' (''C. reticulata'' × ''C.'' ×''sinensis'') * Ugli – (''C. reticulata'' × ''C. maxima'' or ''C.'' ×''paradisi'') * Volkamer lemon – ''Citrus'' ×''volkameriana'' (''C. reticulata'' × ''C. medica'') * Yukou – (''Citrus yuko'') *
Yuzu Yuzu (''Citrus junos'', from Japanese or ) is a citrus fruit and plant in the family Rutaceae of East Asian origin. Yuzu has been cultivated mainly in East Asia, though recently also in New Zealand, Australia, Spain, Italy, and France. ...
– ''Citrus'' ×''junos'' (''C. reticulata'' × ''C.'' ×''cavaleriei'') Other/Unresolved * Djeruk limau – ''Citrus'' ×''amblycarpa'' * Gajanimma, Carabao Lime – ''Citrus'' ×''pennivesiculata'' * Hyuganatsu, Hyuganatsu pumelo – ''Citrus tamurana'' * Ichang lemon – (''C.'' ''cavaleriei'' × ''C. maxima'') *
Kabosu Kabosu (カボス or 臭橙; binomial name: ''Citrus sphaerocarpa'') is a citrus fruit of an evergreen broad-leaf tree in the family Rutaceae. It is popular in Japan, where its juice is used to improve the taste of many dishes, especially cook ...
– ''Citrus'' ×''sphaerocarpa'' * Odichukuthi – ''Citrus Odichukuthi'' from Malayalam * Ougonkan – ''Citrus flaviculpus'' hort ex. Tanaka *
Sakurajima komikan orange The is a type of mandarin orange grown in Japan. "Ko" means "little", and " mikan" a type of citrus cultivar; komikans are unusually small. It is almost the same as the Kishumikan. It is sometimes called a grown on Sakurajima, an active co ...
* Shonan gold – (Ougonkan) ''Citrus flaviculpus'' hort ex. Tanaka × (Imamura unshiu), ''Citrus unshiu'' Marc * Sudachi – ''Citrus'' ×''sudachi'' For hybrids with kumquats, see
citrofortunella 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 ...
. For hybrids with the trifoliate orange, see citrange.


See also

*
Citrus taxonomy 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. Citrus taxonomy is complex and controversial. ...
* Japanese citrus * List of lemon dishes and beverages


References


External links


Effects of pollination on Citrus plants
Pollination of Citrus by Honey Bees
Citrus Research and Education Center
of IFAS (largest citrus research center in world)
Citrus Variety Collection by the University of California


(Mark Rieger, Professor of Horticulture, University of Georgia)

is an organization of citrus Brazilian producers and processors.
''Citrus'' – taxonomy
fruit anatomy at GeoChemBio * {{Authority control Cocktail garnishes Garden plants Citrus fruits Lists of plants Ornamental trees Plants used in bonsai Aurantioideae genera