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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 biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...
of
flowering A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Magnoliophyta, also called angiosperms). The biological function of a flower is to facilitate reproduction, usu ...
tree 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 ...

tree
s and
shrub A shrub (or bush, but this is more of a gardening term) is a small- to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be deciduous or evergreen. They are distinguish ...
s in the rue family,
Rutaceae The Rutaceae is a family, commonly known as the rueRUTACEAE
in BoDD – Botanical Derma ...
. Plants in the genus produce citrus fruits, including important
crop A crop is a plant or animal product that can be grown and harvested extensively for profit or subsistence. Crops may refer either to the harvested parts or to the harvest in a more refined state. Most crops are cultivated in agriculture or aquacul ...
s such as
oranges The orange is the fruit of various citrus species in the family Rutaceae (see list of plants known as orange); it primarily refers to ''Citrus'' × ''sinensis'', which is also called sweet orange, to distinguish it from the related ''Citrus ...
,
lemon The lemon, ''Citrus limon'', is a species of small evergreen tree in the flowering plant family Rutaceae, native to South Asia, primarily Northeast India. The tree's ellipsoidal yellow fruit is used for culinary and non-culinary purposes thr ...

lemon
s,
grapefruit The grapefruit (''Citrus × paradisi'') is a subtropical citrus tree known for its relatively large sour to semisweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit is a citr ...
s,
pomelo The pomelo (), pummelo (), or in scientific terms ''Citrus maxima'' or ''Citrus grandis'', is the largest citrus fruit from the family Rutaceae and the principal ancestor of the grapefruit. It is a natural, i.e., non-hybrid, citrus fruit, na ...
s, and
limes Lime or Limes primarily refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime or Limes may also re ...
. The genus ''Citrus'' is native to
South Asia South Asia is the southern region of Asia, which is defined in both geographical and ethno-cultural terms. The region consists of the countries of Afghanistan, Pakistan, India, Nepal, Bhutan, Bangladesh, the Maldives, and Sri Lanka.;;;;;;;; Top ...

South Asia
,
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. The East Asian states of China, North ...
,
Southeast Asia Southeast Asia or Southeastern Asia is the southeastern subregion of Asia, consisting of the regions that are geographically south of China, east of the Indian subcontinent and north-west of Australia. Southeast Asia is bordered to the north b ...

Southeast Asia
,
Melanesia Melanesia (, ) is a subregion of Oceania in the southwestern Pacific Ocean. It extends from the island of New Guinea in the west to Tonga in the east, and includes the Arafura Sea. The region includes the four independent countries of Fiji, V ...

Melanesia
, 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. It is the largest country in Oceania and the world's sixt ...
. Various citrus species have been utilized and domesticated by indigenous cultures in these areas since ancient times. From there its cultivation spread into
Micronesia Micronesia (, ; from grc, μικρός ''mikrós'' "small" and ''nêsos'' "island") is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It has a close shared cultural history with three other island ...

Micronesia
and
Polynesia Polynesia (, ; from gr, πολύς ''polys'' "many" and gr, νῆσος ''nēsos'' "island") ( to, Faka-Polinisia; mi, Porinihia; haw, Polenekia; fj, Kai-Polinesia; sm, Polenisia; rar, Porinetia) is a subregion of Oceania, made up of more than ...

Polynesia
by the
Austronesian expansion The Austronesian peoples, also sometimes referred to as the Austronesian-speaking peoples, are a large group of various peoples in Taiwan (collectively known as Taiwanese indigenous peoples), Maritime Southeast Asia, Oceania and Madagascar that ...
(c. 3000–1500 BCE); and to the
Middle East The Middle East is a transcontinental region in Afro-Eurasia which generally includes Western Asia (except for Transcaucasia), all of Egypt (mostly in North Africa), and Turkey (partly in Southeast Europe). The term has come into wider usa ...

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 the east ...
(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 Levant ...
, and onwards to
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It comprises the westernmost peninsulas of the continental landmass of Eurasia, and is bordered by the Arctic Ocean to the north, the Atlant ...
.


History

Citrus plants are native to subtropical and tropical regions of Asia,
Island Southeast Asia Maritime Southeast Asia (as opposed to mainland 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, Ins ...
,
Near Oceania Near Oceania is the part of Oceania settled 35,000 years ago, comprising Australia, New Guinea, and northwestern Island Melanesia: the Bismarck Archipelago and the Solomon Islands. Prehistory The great nineteenth-century naturalist Alfred Russel W ...
, and northeastern
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. It is the largest country in Oceania and the world's sixt ...

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. Introgre ...
, 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 (); Sanskrit: ( 'snow') and ( 'abode, temple, dwelling'), is a mountain range in South and East Asia separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has many of Earth's highest ...

Himalayas
, in a region stretching from eastern
Assam 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 . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Man ...

Assam
, northern
Myanmar Myanmar (; my, မြန်မာ ) or Burma ( my, ဗမာ ), officially the Republic of the Union of Myanmar, is a country in Southeast Asia. Myanmar is bordered by Bangladesh and India to its northwest, China to its northeast, Laos and ...
, 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 Chinese ...
. It diverged from a common ancestor with '' Poncirus trifoliata''. 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. References ...
(11.63 to 5.33 mya) resulted in a sudden speciation event. The species resulting from this event include the
citron The citron (''Citrus medica'') is a large fragrant citrus fruit with a thick rind. It is one of the three original citrus fruits from which all other citrus types developed through natural hybrid speciation or artificial hybridization. Though c ...

citron
s (''Citrus medica'') of South Asia; the
pomelo The pomelo (), pummelo (), or in scientific terms ''Citrus maxima'' or ''Citrus grandis'', is the largest citrus fruit from the family Rutaceae and the principal ancestor of the grapefruit. It is a natural, i.e., non-hybrid, citrus fruit, na ...
s (''C. maxima'') of
Mainland Southeast Asia Mainland Southeast Asia (or the Indochinese Peninsula) is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of China and is bordered by the Indian Ocean to the west and the Pacific Ocean to the east. ...
; the
mandarin Mandarin may refer to: * Mandarin (bureaucrat), a bureaucrat of Imperial China (the original meaning of the word) ** by extension, any senior government bureaucrat Language * Mandarin Chinese, branch of Chinese spoken in northern and southwester ...
s (''C. reticulata''),
kumquat Kumquats (or cumquats in Australian English, ; ''Citrus japonica'') are a group of small fruit-bearing trees in the flowering plant family Rutaceae. They were previously classified as forming the now-historical genus ''Fortunella'', or placed wit ...
s (''C. japonica''),
mangshanyegan The mangshanyegan (; ''Citrus mangshanensis'') 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 man ...
(''C. mangshanensis''), and
ichang papeda ''Citrus cavaleriei'', the Ichang papeda (Chinese: 宜昌橙), is a slow-growing species of papeda that has characteristic lemon-scented foliage and flowers. It is native to southwestern and west-central China and is likely named for the city of ...
s (''C. cavaleriei'') of southeastern
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population of around 1.4 billion. Covering approximately 9.6 million square kilometers (3.7 million m ...
; the
kaffir lime ''Citrus hystrix'', called the kaffir lime, makrut lime (, ), Thai lime or Mauritius papeda, is a citrus fruit native to tropical Southeast Asia and southern China. Its fruit and leaves are used in Southeast Asian cuisine and its essential oil is ...
s (''C. hystrix'') of
Island Southeast Asia Maritime Southeast Asia (as opposed to mainland 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, Ins ...
; and the biasong and samuyao (''C. micrantha'') of the
Philippines The Philippines (; fil, Pilipinas or ''Filipinas'' ), officially the Republic of the Philippines ( fil, Republika ng Pilipinas), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republika sang ...

Philippines
. 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. Neighbouring countries include the People's Republic of China (PRC) to the northwest, Japan to the northeast, and the Philippines to the south. The main island of Ta ...
and
Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white rectangle , image_coat = Imperial Seal of Japan.svg , alt_coat = Golden circle subdivided ...
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 * Early B ...
(5.33 to 3.6 mya), resulting in the
tachibana orange The tachibana orange (''Citrus tachibana,'' or ''Citrus reticulata tachibana'') 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 t ...
(''C. tachibana''); and beyond the
Wallace Line 250px, Wallace's Line delineates Australian and Southeast Asian fauna. The probable extent of land at the time of the last glacial maximum, when the sea level was more than lower than today, is shown in grey. The deep water of the Lombok Strait b ...
into
Papua New Guinea Papua New Guinea (PNG; , ; tpi, Papua Niugini; ho, Papua Niu Gini; tcs, Op Deudai), officially the Independent State of Papua New Guinea ( tpi, Independen Stet bilong Papua Niugini; ho, Independen Stet bilong Papua Niu Gini), is a country in ...
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. It is the largest country in Oceania and the world's sixt ...

Australia
during the
Early Pleistocene The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest (or lowest) division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span ...
(2.5 million to 800,000 years ago), where further speciation events occurred resulting in the
Australian lime Australian limes are species of the plant genus ''Citrus'' that are native to Australia and Papua New Guinea. These species were formerly included in the genera ''Microcitrus'' and ''Eremocitrus''. They have been used as a food source by indigenou ...
s. The earliest introductions of citrus species by human migrations was during the
Austronesian expansion The Austronesian peoples, also sometimes referred to as the Austronesian-speaking peoples, are a large group of various peoples in Taiwan (collectively known as Taiwanese indigenous peoples), Maritime Southeast Asia, Oceania and Madagascar that ...
(c. 3000–1500 BCE), where ''
Citrus hystrix ''Citrus hystrix'', called the kaffir lime, makrut lime (, ), Thai lime or Mauritius papeda, is a citrus fruit native to tropical Southeast Asia and southern China. Its fruit and leaves are used in Southeast Asian cuisine and its essential oil is ...
'', ''
Citrus macroptera ''Citrus macroptera'', also known as hatkhora, satkara, shatkora, hatxora, cabuyao,Peter Hanelt (ed.) 2001 ''Mansfeld's encyclopedia of agricultural and horticultural crops (except ornamentals), first English edition''. Springerin Google Books/ref ...
'', and ''
Citrus maxima The pomelo (), pummelo (), or in scientific terms ''Citrus maxima'' or ''Citrus grandis'', is the largest citrus fruit from the family Rutaceae and the principal ancestor of the grapefruit. It is a natural, i.e., non-hybrid, citrus fruit, na ...
'' were among the
canoe plants 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 (3500 to 2000 BC). These migrations were accompanied by a ...
carried by
Austronesian Austronesian may refer to: *The Austronesian languages *The historical Austronesian peoples who carried Austronesian languages on their migrations {{disambiguation ...
voyagers eastwards into
Micronesia Micronesia (, ; from grc, μικρός ''mikrós'' "small" and ''nêsos'' "island") is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It has a close shared cultural history with three other island ...

Micronesia
and
Polynesia Polynesia (, ; from gr, πολύς ''polys'' "many" and gr, νῆσος ''nēsos'' "island") ( to, Faka-Polinisia; mi, Porinihia; haw, Polenekia; fj, Kai-Polinesia; sm, Polenisia; rar, Porinetia) is a subregion of Oceania, made up of more than ...

Polynesia
. The citron (''
Citrus medica The citron (''Citrus medica'') is a large fragrant citrus fruit with a thick rind. It is one of the three original citrus fruits from which all other citrus types developed through natural hybrid speciation or artificial hybridization. Though c ...
'') 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 ( fa, ایران ), also called Persia and officially the Islamic Republic of Iran ( fa, جمهوری اسلامی ایران ), is a country in Western Asia. It is bordered to the northwest by Armenia and Azerbaijan, to the north by ...

Persia
, 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, it is equivalent to the historical region of Syria, which included present-day ...

Levant
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") is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate. At , the A ...
and
Ptolemaic Egypt#REDIRECT Ptolemaic Kingdom#REDIRECT Ptolemaic Kingdom {{R from other capitalisation ...
{{R from other capitalisation ...
into
North 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 Mauritania in the west, to Egypt's Su ...
. 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 Hala Sultan Tekke or the Mosque of Umm Haram ( el, Τεκές Χαλά Σουλτάνας ''Tekés Chalá Soultánas''; tr, Hala Sultan Tekkesi) is a mosque and tekke complex on the west bank of Larnaca Salt Lake, in Larnaca, Cyprus. Umm Haram ( tr, ...
site of
Cyprus Cyprus ; tr, Kıbrıs (), officially called the Republic of Cyprus,, , lit: Republic of Cyprus is an island nation in the eastern Mediterranean Sea. It is the third largest and third most populous island in the Mediterranean, and is locate ...
, dated to around 1200 BCE. Other archaeobotanical evidence include pollen from
Carthage Carthage was the capital city of the ancient Carthaginian civilization, on the eastern side of the Lake of Tunis in what is now Tunisia. Carthage was the most important trading hub of the Ancient Mediterranean and one of the most affluent cities o ...

Carthage
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 buried und ...
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 ''Theόphrastos''; c. 371c. 287 BC), a Greek native of Eresos in Lesbos,Gavin Hardy and Laurence Totelin, ''Ancient Botany'', Routledge, 2015, p. 8. was the successor to Aristotle in the Peripatetic ...

Theophrastus
, c. 310 BCE. The agronomists of
classical Rome In historiography, ancient Rome is Roman civilization from the founding of the Italian city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD, encompassing the Roman Kingdom (753 BC–509 BC), Rom ...
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 Portuguese may refer to: * anything of, from, or related to the country and nation of Portugal ** Portuguese cuisine, traditional foods ** Portuguese language, a Romance language *** Portuguese dialects, variants of the Portuguese language ** Portug ...
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 , Moscow (1760s). built by Frederick William IV of Prussia in Potsdam in the mid-19th century. , Belgium (ca.1820), is the oldest part of the monumental Royal Greenhouses of Laeken. An orangery or orangerie was a room or a dedicated building on ...
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 branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became the dominant language ...
, where it referred to either the plant now known as
citron The citron (''Citrus medica'') is a large fragrant citrus fruit with a thick rind. It is one of the three original citrus fruits from which all other citrus types developed through natural hybrid speciation or artificial hybridization. Though c ...

citron
(''C. medica'') or a conifer tree (''
Thuja ''Thuja'' ( ) is a genus of coniferous trees in the Cupressaceae (cypress family). There are five species in the genus, two native to North America and three native to eastern Asia. The genus is monophyletic and sister to ''Thujopsis''. Members ar ...
''). 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 period ...
word for
cedar Cedar may refer to: Trees and plants *''Cedrus'', common English name cedar, a genus of coniferous trees in the plant family Pinaceae *Cedar (plant), a list of trees and plants known as cedar Places United States * Cedar, Arizona * Cedar, India ...
, 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 Romance (from Vulgar Latin , "in the Roman language", i.e., "Latin") may refer to: Common meanings * Romance (love), emotional attraction towards another person and the courtship behaviors undertaken to express the feelings * Romance languages, a ...

Romance
loanword A loanword (also loan word or loan-word) is a word as adopted from one language (the donor language) and incorporated into another language without translation. This is in contrast to cognates, which are words in two or more languages that are simi ...
''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) 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 The trifoliate orange, ''Citrus trifoliata'' or ''Poncirus trifoliata'', is a member of the family Rutaceae. Whether the species should be considered to belong to its own genus, ''Poncirus'' or included in the genus ''Citrus'' is debated. The spec ...
), 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 Chloroplasts are organelles that conduct photosynthesis, where the photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it in the energy-storage molecules ATP and NADPH while freeing oxygen from water ...

chloroplast
s. A DNA study published in ''
Nature Nature, in the broadest sense, is the natural, physical, material 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. Al ...
'' in 2018 concludes that the genus ''Citrus'' first evolved in the foothills of the
Himalaya The Himalayas, or Himalaya (); Sanskrit: ( 'snow') and ( 'abode, temple, dwelling'), is a mountain range in South and East Asia separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has many of Earth's highest ...
s, in the area of
Assam 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 . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Man ...

Assam
(
India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the second-most populous country, the seventh-largest country by land area, and the most populous democracy in the world. Bounded by the Indian Oce ...

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 Chinese ...
(
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population of around 1.4 billion. Covering approximately 9.6 million square kilometers (3.7 million m ...
), and northern
Myanmar Myanmar (; my, မြန်မာ ) or Burma ( my, ဗမာ ), officially the Republic of the Union of Myanmar, is a country in Southeast Asia. Myanmar is bordered by Bangladesh and India to its northwest, China to its northeast, Laos and ...
. The three ancestral (sometimes characterized as "original" or "fundamental") species in the genus ''Citrus'' associated with modern ''Citrus'' cultivars are the
mandarin orange The mandarin orange (''Citrus reticulata''), also known as the mandarin or mandarine, is a small citrus tree fruit. Treated as a distinct species of orange, it is usually eaten plain or in fruit salads. Tangerines are a group of orange-coloured ci ...
,
pomelo The pomelo (), pummelo (), or in scientific terms ''Citrus maxima'' or ''Citrus grandis'', is the largest citrus fruit from the family Rutaceae and the principal ancestor of the grapefruit. It is a natural, i.e., non-hybrid, citrus fruit, na ...
, and
citron The citron (''Citrus medica'') is a large fragrant citrus fruit with a thick rind. It is one of the three original citrus fruits from which all other citrus types developed through natural hybrid speciation or artificial hybridization. Though c ...

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: , literally "obtained by digging") 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 ...
leaf from the
Pliocene The Pliocene ( ; also Pleiocene) Epoch is the epoch in the geologic timescale that extends from 5.333 million to 2.58Valdarno The Valdarno is the valley of the river Arno, although it does not apply to the entire basin of the river. The usage of the term generally excludes Casentino and the valleys formed by the major tributaries, such as the Val di Chiana, the Val d'Ambr ...
(
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a continental part, delimited by the Alps, a peninsula and several islands surrounding it. Italy is located in Southern Europ ...
) is described as †''Citrus meletensis''. In
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population of around 1.4 billion. Covering approximately 9.6 million square kilometers (3.7 million m ...
, 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 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 cancella ...
, 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 author Charles Lyell; its name comes from the Greek words (', "less") and (', "new") and means "less recent" becaus ...
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 (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
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 trees ...
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 appropriate sexe ...
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 cutting ...
), 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 natural, physical, material 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. Al ...
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. Cultivated citrus are ...
s include commercially important
fruit In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate seeds. Edible fruits, in particular, have propagated ...
such as oranges,
grapefruit The grapefruit (''Citrus × paradisi'') is a subtropical citrus tree known for its relatively large sour to semisweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit is a citr ...
,
lemon The lemon, ''Citrus limon'', is a species of small evergreen tree in the flowering plant family Rutaceae, native to South Asia, primarily Northeast India. The tree's ellipsoidal yellow fruit is used for culinary and non-culinary purposes thr ...

lemon
s, limes, and some
tangerine The tangerine (''Citrus reticulata L. var.'', sometimes referred as ''Citrus x tangerina'') is a group of orange-coloured citrus fruit consisting of hybrids of mandarin orange (''Citrus reticulata'') with some pomelo contribution. The name was ...
s. Apart from these core citrus species,
Australian lime Australian limes are species of the plant genus ''Citrus'' that are native to Australia and Papua New Guinea. These species were formerly included in the genera ''Microcitrus'' and ''Eremocitrus''. They have been used as a food source by indigenou ...
s and the recently discovered
mangshanyegan The mangshanyegan (; ''Citrus mangshanensis'') 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 man ...
are grown.
Kumquat Kumquats (or cumquats in Australian English, ; ''Citrus japonica'') are a group of small fruit-bearing trees in the flowering plant family Rutaceae. They were previously classified as forming the now-historical genus ''Fortunella'', or placed wit ...
s and '' Clymenia'' spp. are now generally considered to belong within the genus ''Citrus''. Trifoliate orange, which is often used as commercial
rootstock A rootstock is part of a plant, often an underground part, from which new above-ground growth can be produced. It could also be described as a stem with a well developed root system, to which a bud from another plant is grafted. It can refer to a r ...
, 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 γενετικός () "origin, source, birth") is a part of systematics that addresses the inference of the evolutionary history and relationships among or wit ...

Phylogenetic
analysis suggests the species of ''
Oxanthera ''Oxanthera'' is a genus of flowering plants in the citrus family, Rutaceae. They are endemic to New Caledonia. They are known commonly as false oranges. Phylogenetic analysis has shown these species to cluster in the same clade as ''Clymenia'' ...
'' from
New Caledonia ) , anthem = "Soyons unis, devenons frères" , 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 , subdivisio ...

New Caledonia
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.


Description


Tree

These plants are large
shrub A shrub (or bush, but this is more of a gardening term) is a small- to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be deciduous or evergreen. They are distinguish ...
s 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, which c ...
leaves A leaf (plural leaves) is the principal lateral appendage of the vascular plant stem, usually borne above ground and specialized for photosynthesis. The leaves and stem together form the shoot. Leaves are collectively referred to as foliag ...

leaves
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 Magnoliophyta, also called angiosperms). The biological function of a flower is to facilitate reproduction, usu ...
s are solitary or in small
corymb Corymb is a botanical term for an inflorescence with the flowers growing in such a fashion that the outermost are borne on longer pedicels than the inner, bringing all flowers up to a common level. A corymb has a flattish top with a superficial res ...
s, 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 In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate seeds. Edible fruits, in particular, have propagated ...
is a
hesperidium Etymology Carl Linnaeus gave the name Hesperideæ to an order containing the genus ''Citrus'', in allusion to the golden apples of the Hesperides. Development The outer ovary wall becomes the thick spongy layer of the rind, while the inner ovary ...
, a specialised berry, globose to elongated, long and diameter, with a leathery rind or "peel" called a
pericarp Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. In fleshy fruits, the outer layer (typically edible) is the pericarp, which is the tissue that develops from the ...
. The outermost layer of the pericarp is an "exocarp" called the
flavedo Fruit anatomy is the plant anatomy of the internal structure of fruit. Fruits are the mature ovary or ovaries of one or more flowers. In fleshy fruits, the outer layer (typically edible) is the pericarp, which is the tissue that develops from the ...
, 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'' usual ...
filled with
juice vesiclesThe juice vesicles, also known as citrus kernels, (in aggregate, pulp) of a citrus fruit are the membranous content of the fruit's endocarp. All fruits from the Citranae subtribe, subfamily Aurantioideae, and family Rutaceae have juice vesicles. The ...
, or "pulp". From the endocarp, string-like "hairs" extend into the locules, which provide nourishment to the fruit as it develops. Many citrus
cultivar '' 'Pink Whirls' A cultivar selected for its intriguing and colourful flowers A cultivarCultivar () has two denominations as explained in ''#Formal definition, Formal definition''. When referring to a taxon, the word does not apply to an individ ...
s have been developed to be seedless (see
nucellar embryony Most commercial citrus varieties produce mainly nucellar seedlings. 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 ...
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 are act ...
) 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 diets. Chemically, flavonoids have the general ...
s and
limonoidChemical structure of the prototypical limonoid limonin Limonoids are phytochemicals of the triterpenoid class which abundant in sweet or sour-scented citrus fruit and other plants of the families Cucurbitaceae, Rutaceae, and Meliaceae. Certain lim ...
s (which in turn are
terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes are further c ...
s) contained in the rind, and most are juice-laden. The juice contains a high quantity of
citric acid Citric acid is a weak organic acid that has the molecular formula C6H8O7. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. More than ...
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 Juice is a drink made from the extraction or pressing of the natural liquid contained in fruit and vegetables. It can also refer to liquids that are flavored with concentrate or other biological food sources, such as meat or seafood, such as c ...
, or preserved in
marmalade Marmalade is a fruit preserve made from the juice and peel of citrus fruits boiled with sugar and water. The well-known version is made from bitter orange, but it is also made from lemons, limes, grapefruits, mandarins, sweet oranges, bergamo ...
s and
pickles Pickles may refer to: Food * Pickles, a name for a pickled cucumber in the United States and Canada * Pickle, a sweet, vinegary pickled chutney popular in Britain, such as Branston Pickle, also known as "sweet pickle" or "ploughman's pickle" * S ...
. They are also good sources of
vitamin C Vitamin C (also known as ascorbic acid and ascorbate) is a vitamin found in various foods and sold as a dietary supplement. It is used to prevent and treat scurvy. Vitamin C is an essential nutrient involved in the repair of tissue and the en ...
. 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 * Isosakur ...
s and
flavone Flavones (from Latin ''flavus'' "yellow") are a class of flavonoids based on the backbone of 2-phenylchromen-4-one (2-phenyl-1-benzopyran-4-one) (as shown in the first image of this article). Flavones are common in foods, mainly from spices, and so ...
s.


Cultivation

Citrus trees hybridise very readily – depending on the
pollen Pollen Tube Diagram Pollen is a powdery substance consisting of pollen grains which are male microgametophytes of seed plants, which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gamet ...
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 key l ...
'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 success ...
the desired fruiting
cultivar '' 'Pink Whirls' A cultivar selected for its intriguing and colourful flowers A cultivarCultivar () has two denominations as explained in ''#Formal definition, Formal definition''. When referring to a taxon, the word does not apply to an individ ...
s onto
rootstocks A rootstock is part of a plant, often an underground part, from which new above-ground growth can be produced. It could also be described as a stem with a well developed root system, to which a bud from another plant is grafted. It can refer to a r ...
selected for disease resistance and hardiness. The colour of citrus fruits only develops in climates with a (
diurnal Diurnal ("daily") may refer to: General * Diurnal cycle, any pattern that recurs daily ** Diurnality, the behavior of animals and plants that are active in the daytime * Diurnal phase shift, a phase shift of electromagnetic signals * Diurnal tempe ...
) 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 Ripening is a process in fruits that causes them to become more palatable. In general, fruit becomes sweeter, less green (typically "redder"), and softer as it ripens. Even though the acidity of fruit increases as it ripens, the higher acidity leve ...
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 gas) t ...
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, recently also in Australia, Spain, Italy and France. It is believed to have orig ...
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
citrange The citrange is a citrus hybrid of the sweet orange and the trifoliate orange. The purpose of this cross was to attempt to create a cold hardy citrus tree (which is the nature of a trifoliate), with delicious fruit like those of the sweet orange. ...
s). 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 RangesThe 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 refere ...
. 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 The Food and Agriculture Organization of the United Nations (FAO)french: Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is a specialized agency of ...
, world production of all citrus fruits in 2016 was 124 million tons, with about half of this production as oranges. According to the
United Nations Conference on Trade and Development The United Nations Conference on Trade and Development (UNCTAD) was established in 1964 as a permanent intergovernmental body. UNCTAD is the part of the United Nations Secretariat dealing with trade, investment, and development issues. The or ...
(UNCTAD), citrus production grew during the early
21st century The 21st (twenty-first) century is the current century in the ''Anno Domini'' era or Common Era, in accordance with the Gregorian calendar. It began on January 1, 2001 (MMI), and will end on December 31, 2100 (MMC). The 21st century is the first ...
mainly by the increase in
cultivation Cultivation may refer to: * The state of having or expressing a good education (bildung), refinement, culture, or high culture * Gardening * Agriculture, the cultivation and breeding of animals, plants and fungi * Fungiculture, the process of produ ...
areas, improvements in transportation and packaging, rising incomes and
consumer A consumer is a person or a group who intends to order, orders, or uses purchased goods, products, or services primarily for personal, social, family, household and similar needs, not directly related to entrepreneurial or business activities. ...
preference In psychology, economics and philosophy, a 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. Preference can also be used in insolven ...

preference
for healthy foods. In 2019-20, world production of oranges was estimated to be 47.5 million tons, 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 , Moscow (1760s). built by Frederick William IV of Prussia in Potsdam in the mid-19th century. , Belgium (ca.1820), is the oldest part of the monumental Royal Greenhouses of Laeken. An orangery or orangerie was a room or a dedicated building on ...
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 Mount Vernon is an American landmark and former plantation of George Washington, the first President of the United States, and his wife, Martha. The estate is on the banks of the Potomac River in Fairfax County, Virginia, near Alexandria, acros ...
. 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 c ...

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.


Pests and diseases

Citrus plants are very liable to infestation by
aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A typi ...
s,
whitefly Whiteflies are Hemipterans that typically feed on the undersides of plant leaves. They comprise the family Aleyrodidae, the only family in the superfamily Aleyrodoidea. More than 1550 species have been described. Description and taxonomy The Aley ...
, 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 superfamily Coccoidea. Adult females typically have soft bodies and no limbs, a ...

scale insect
s (e.g. California red scale). Also rather important are the viral infections to which some of these
ectoparasite Parasitism is a symbiotic 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 has ...
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 t ...
'', 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 calle
Huanglongbing (HLB)
also known as citrus greening disease. 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 Food science is the basic science and applied science of food; its scope starts at overlap with agricultural science and nutritional science and leads through the scientific aspects of food safety and food processing, informing the development of ...
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, and has the th ...
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
) is a city of both 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. The lar ...
e of
Lepidoptera Lepidoptera ( , from Ancient Greek ''lepís'' “scale” + ''pterón'' “wing”) 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 famili ...
(
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 comprises the ...
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 whi ...
) species such as the
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 species b ...
(''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 D ...
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 down to Panama. The obsol ...
(''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, 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 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, 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.


Uses


Culinary

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. 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 peel (fruit), rind and essential oil, oil of the fruit is generally bitter, especially when cooked, so is often combined with sugar. The juice vesicles, 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 (food), 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 (ingredient), 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 semisweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink. Grapefruit is a citr ...
, Lime (fruit), lime, and
lemon The lemon, ''Citrus limon'', is a species of small evergreen tree in the flowering plant family Rutaceae, native to South Asia, primarily Northeast India. The tree's ellipsoidal yellow fruit is used for culinary and non-culinary purposes thr ...

lemon
, and a half Orange (fruit), orange (clockwise from top) File:Calamansi (sliced) - Philippines.jpg, Calamansi, a ubiquitous part of traditional Philippine condiments, dipping sauces and condiments in Philippine cuisine File:Citrus aurantiifolia in Kadavoor.jpg, ''Citrus aurantifolia'' in Kerala File:Pomeranzen.jpg, Ripe bitter oranges (''Citrus × aurantium'') from Asprovalta


Phytochemicals and research

Some ''Citrus'' species contain significant amounts of the phytochemical class called 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, 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, a linear furanocoumarin derived from psoralen. This claim has been confirmed for lime and Bergamot orange, 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, 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 crenatifolia'' – species name is unresolved, from Sri Lanka * ''Citrus japonica'' – kumquats, from East Asia ranging into Southeast Asia (sometimes separated into four-five ''Fortunella'' species) * ''Citrus mangshanensis'' – species name is unresolved, from Hunan Province, China * ''pomelo, Citrus maxima'' – pomelo (pummelo, shaddock), from the
Island Southeast Asia Maritime Southeast Asia (as opposed to mainland 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, Ins ...
* ''
Citrus medica The citron (''Citrus medica'') is a large fragrant citrus fruit with a thick rind. It is one of the three original citrus fruits from which all other citrus types developed through natural hybrid speciation or artificial hybridization. Though c ...
'' – citron, from India * ''Byeonggyul, Citrus platymamma'' – ''byeonggyul'', from Jejudo, Jeju Island, Korea * ''Citrus reticulata'' – mandarin orange, from China * ''Citrus trifoliata'' – trifoliate orange, from Korea and adjacent China (often separated as ''Poncirus'') *
Australian lime Australian limes are species of the plant genus ''Citrus'' that are native to Australia and Papua New Guinea. These species were formerly included in the genera ''Microcitrus'' and ''Eremocitrus''. They have been used as a food source by indigenou ...
s **''Citrus australasica'' – Australian finger lime ** ''Citrus australis'' – Australian round lime ** ''Citrus glauca'' – Australian desert lime ** ''Citrus garrawayi '' – Mount White lime ** ''Citrus gracilis'' – Kakadu lime or Humpty Doo lime ** ''Citrus inodora'' – Russel River lime ** ''Citrus maideniana'' - Maiden's Australian lime ** ''Citrus warburgiana '' – New Guinea wild lime ** ''Citrus wintersii '' – Brown River finger lime * Papeda (citrus), Papedas, including **''Citrus halimii'' – ''limau kadangsa'', ''limau kedut kera'', from Thailand and Malay Peninsula, Malaya ** ''
Citrus hystrix ''Citrus hystrix'', called the kaffir lime, makrut lime (, ), Thai lime or Mauritius papeda, is a citrus fruit native to tropical Southeast Asia and southern China. Its fruit and leaves are used in Southeast Asian cuisine and its essential oil is ...
'' – Kaffir lime, ''makrut'', from
Mainland Southeast Asia Mainland Southeast Asia (or the Indochinese Peninsula) is the continental portion of Southeast Asia. It lies east of the Indian subcontinent and south of China and is bordered by the Indian Ocean to the west and the Pacific Ocean to the east. ...
to
Island Southeast Asia Maritime Southeast Asia (as opposed to mainland 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, Ins ...
** ''Citrus cavaleriei'' – Ichang papeda from southern China ** ''Citrus celebica'' - Celebes papeda ** ''Citrus indica'' – Indian wild orange, from the Indian subcontinent ** ''Citrus latipes'' – Citrus latipes, Khasi papeda, from
Assam 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 . The state is bordered by Bhutan and Arunachal Pradesh to the north; Nagaland and Man ...

Assam
, Meghalaya, Burma ** ''Citrus longispina'' - Megacarpa papeda, winged lime, blacktwig lime ** ''Citrus macrophylla'' - Alemow ** ''
Citrus macroptera ''Citrus macroptera'', also known as hatkhora, satkara, shatkora, hatxora, cabuyao,Peter Hanelt (ed.) 2001 ''Mansfeld's encyclopedia of agricultural and horticultural crops (except ornamentals), first English edition''. Springerin Google Books/ref ...
'' - Melanesian papeda from Indochina to Melanesia ** ''Citrus micrantha, Citrus westeri'' - ''biasong'' or ''samuyao'' from the southern Philippines ** ''Citrus webberi'' - Kalpi, Malayan lemon


Hybrids and cultivars

File:Clementinepeeled.jpg, Clementines (''Citrus'' ×''clementina'') have thinner skins than oranges. 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 – ''Citrus'' ×''paradisi'' (''C. maxima'' × ''C.'' ×''sinensis'') * Haruka (citrus), Haruka - ''Citrus tamurana'' x ''natsudaidai'' * Hassaku orange - (''Citrus hassaku'') * Ichang lemon - (''Citrus wilsonii'') * Imperial lemon – (''C.'' ×''limon'' × ''C.'' ×''paradisi'') * Kawachi Bankan - (''Citrus kawachiensis'') * Kinnow – (''C.'' ×''nobilis'' × ''C.'' ×''deliciosa'') * Kiyomi – (''C.'' ×''sinensis'' × ''C.'' ×''unshiu'') * Minneola tangelo – (''C. reticulata'' × ''C.'' ×''paradisi'') * Orangelo, Chironja – (''C.'' ×''paradisi'' × ''C.'' ×''sinensis'') * Oroblanco, Sweetie – (''C. maxima'' × ''C.'' ×''paradisi'') * Sweet orange – ''Citrus'' ×''sinensis'' (probably ''C. maxima'' × ''C. reticulata'') * Tangelo – ''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. ''sarcodactylus'', a fingered citron. * Citron varieties with sour juice vesicles, pulp – Diamante citron, Florentine citron, Greek citron and Balady citron * Citron varieties with sweet pulp – Corsican citron and Moroccan citron. * Etrog, a group of citron cultivars that are traditionally used for a Jewish ritual. ''Etrog'' is Hebrew for citron in general. * Fernandina (fruit), 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 key l ...
, Tahiti lime – ''C.'' ×''latifolia'' (''C.'' ×''aurantiifolia'' × ''C.'' ×''limon'') * Limetta, Sweet Lemon, Sweet Lime, mosambi – ''Citrus'' ×''limetta'' (''C. medica'' × ''C.'' ×''aurantium'') * Lumia (citrus), Lumia – several distinct pear shaped lemon-like hybrids * Pompia – ''Citrus medica tuberosa'' Risso & Poiteau, 1818 (''C. medica'' × ''C.'' ×''aurantium''), native to Sardinia, genetically synonymous with Rhobs el Arsa. * Rhobs el Arsa – 'bread of the garden', ''C. medica'' × ''C.'' ×''aurantium'', from Morocco. * Yemenite citron – 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 '' 'Pink Whirls' A cultivar selected for its intriguing and colourful flowers A cultivarCultivar () has two denominations as explained in ''#Formal definition, Formal definition''. When referring to a taxon, the word does not apply to an individ ...
s * Calamansi, Calamondin – (''Citrus reticulata'' × ''Citrus japonica'') * Cam sành – (''C. reticulata'' × ''C.'' ×''sinensis'') * Chinotto – ''Citrus'' ×''aurantium'' var. ''myrtifolia'' or ''Citrus'' ×''myrtifolia'' * Kiyomi, ChungGyun – ''Citrus reticulata'' cultivar * Clementine – ''Citrus'' ×''clementina'' * Cleopatra Mandarin – ''Citrus'' ×''reshni'' * Dekopon, Siranui – ''Citrus reticulata'' cv. 'Dekopon' (ChungGyun × Ponkan) * Daidai – ''Citrus'' ×''aurantium'' var. ''daidai'' or ''Citrus'' ×''daidai'' * 'Encore' mandarin, Encore - ((''Citrus reticulata'' x ''sinensis'') x ''C. deliciosa'') * Grapefruit – ''Citrus'' ×''paradisi'' (''C. maxima'' × ''C.'' ×''sinensis'') * Hermandina – ''Citrus reticulata'' cv. 'Hermandina' * Imperial lemon – ((''C. maxima'' × ''C. medica'') × ''C.'' ×''paradisi'') * Iyokan, ''anadomikan'' – ''Citrus'' ×''iyo'' * Jabara (citrus), Jabara - (''Citrus jabara'') * Kanpei - (''Citrus reticulata'' 'Kanpei') * Kinkoji unshiu - (''Citrus obovoidea'' x ''unshiu'') * Kinnow, Wilking – (''C.'' ×''nobilis'' × ''C.'' ×''deliciosa'') * Kishumikan - (''Citrus kinokuni'') * Kiyomi – (''C. sinensis'' × ''C.'' ×''unshiu'') * Kobayashi mikan - (''Citrus natsudaidai'' x ''unshiu'') * Koji orange - (''Citrus leiocarpa'') * Kuchinotsu No.37 - ('Kiyomi' x 'Encore' mandarin, 'Encore') * Laraha – 'C.'' ×''aurantium'' ssp. ''currassuviencis'' * Citrus x deliciosa, 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 (fruit), Murcott - (''C. reticulata'' x ''sinensis'') * Naartjie – (''C. reticulata'' × ''C. nobilis'') * Nova mandarin, Clemenvilla * Orangelo, Chironja – (''C.'' ×''paradisi'' × ''C.'' ×''sinensis'') * Oroblanco, Sweetie (fruit), Sweetie – (''C. maxima'' × ''C.'' ×''paradisi'') * – ''Citrus'' ×''limettioides'' Chōzaburō Tanaka, Tanaka (''C. medica'' × ''C.'' ×''sinensis'') * Ponkan – ''Citrus reticulata'' cv. 'Ponkan' * Rangpur (fruit), Rangpur, Lemanderin, Mandarin Lime – ''Citrus'' ×''limonia'' (''C. reticulata'' × ''C. medica'') * Reikou - (Kuchinotsu No.37 x 'Murcott') * Rough lemon – ''Citrus'' ×''jambhiri'' Lush. (''C. reticulata'' × ''C. medica'') * Sanbokan - ''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.) Chōzaburō Tanaka, Tanaka or ''C. reticulata'' var. ''tachibana'' * Tangelo – ''Citrus'' ×''tangelo'' (''C. reticulata'' × ''C. maxima'' or ''C.'' ×''paradisi'') * Tangerine – ''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 (Japanese citrus), Yukou - (''Citrus yuko'') * Yuzu – ''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 – ''Citrus'' ×''sphaerocarpa'' * Odichukuthi – ''Citrus Odichukuthi'' from Malayalam * Ougonkan – ''Citrus flaviculpus'' hort ex. Tanaka * Sakurajima komikan orange * Shonan gold – (Ougonkan) ''Citrus flaviculpus'' hort ex. Tanaka × (Imamura unshiu), ''Citrus unshiu'' Marc * Sudachi – ''Citrus'' ×''sudachi'' For hybrids with kumquats, see citrofortunella. For hybrids with the trifoliate orange, see
citrange The citrange is a citrus hybrid of the sweet orange and the trifoliate orange. The purpose of this cross was to attempt to create a cold hardy citrus tree (which is the nature of a trifoliate), with delicious fruit like those of the sweet orange. ...
.


See also

* Citrus taxonomy * 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 Institute of Food and Agricultural Sciences, 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 Citrus, Cocktail garnishes Garden plants Lists of foods, Citrus fruits Lists of plants Ornamental trees Plants used in bonsai Rutaceae genera