''Citrus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of flowering trees and

shrub A shrub or 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 trees by their multiple ...

s in the family

Rutaceae The Rutaceae () is a family (biology), family, commonly known as the rueRUTACEAE
in Bo ...

. Plants in the genus produce citrus fruits, including important crops such as oranges, mandarins,

lemon The lemon (''Citrus'' × ''limon'') is a species of small evergreen tree in the ''Citrus'' genus of the flowering plant family Rutaceae. A true lemon is a hybrid of the citron and the bitter orange. Its origins are uncertain, but some ...

s, grapefruits, pomelos, and limes. ''Citrus'' is native to South Asia, East Asia, Southeast Asia,

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

, and Australia.

Indigenous people There is no generally accepted definition of Indigenous peoples, although in the 21st century the focus has been on self-identification, cultural difference from other groups in a state, a special relationship with their traditional territ ...

in these areas have used and domesticated various species since ancient times. Its cultivation first spread into

Micronesia Micronesia (, ) is a subregion of Oceania, consisting of approximately 2,000 small islands in the Northwestern Pacific Ocean. It has a close shared cultural history with three other island regions: Maritime Southeast Asia to the west, Poly ...

and

Polynesia Polynesia ( , ) is a subregion of Oceania, made up of more than 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are called Polynesians. They have many things in ...

through the Austronesian expansion (–1500 BCE). Later, it was spread 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 east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

() via the incense trade route, and from Europe to the Americas. Renowned for their highly fragrant aromas and complex flavor, citrus are among the most popular fruits in cultivation. With a propensity to hybridize between species, making their taxonomy complicated, there are numerous varieties encompassing a wide range of appearance and fruit flavors.

Evolution

Evolutionary history

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 ''Poncirus'' group (such as the trifoliate orange), which some taxonomies consider a separate genus and others include in ''Citrus'' ''Poncirus'' 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, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

s. A DNA study published in ''

Nature Nature is an inherent character or constitution, particularly of the Ecosphere (planetary), ecosphere or the universe as a whole. In this general sense nature refers to the Scientific law, laws, elements and phenomenon, phenomena of the physic ...

'' in 2018 concludes that the genus ''Citrus'' 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 Earth's highest peaks, including the highest, Mount Everest. More than 100 pea ...

s, in the area of

Assam Assam (, , ) is a state in Northeast India, northeastern India, south of the eastern Himalayas along the Brahmaputra Valley, Brahmaputra and Barak River valleys. Assam covers an area of . It is the second largest state in Northeast India, nor ...

(India), western

Yunnan Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...

(China), and northern

Myanmar Myanmar, officially the Republic of the Union of Myanmar; and also referred to as Burma (the official English name until 1989), is a country in northwest Southeast Asia. It is the largest country by area in Mainland Southeast Asia and has ...

. The three ancestral species in the genus ''Citrus'' associated with modern ''Citrus'' cultivars are the mandarin orange, pomelo, and

citron The citron (''Citrus medica''), historically cedrate, is a large fragrant citrus fruit with a thick Peel (fruit), rind. It is said to resemble a 'huge, rough lemon'. It is one of the Citrus taxonomy#Citrons, original citrus fruits from which al ...

. Almost all of the common commercially important citrus fruits (sweet oranges,

s, grapefruit, limes, and so on) are hybrids between these three species, their main progenies, and other wild ''Citrus'' species within the last few thousand years. Citrus plants are native to subtropical and tropical regions of Asia, Island Southeast Asia, Near Oceania, and northeastern and central 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. Introg ...

, 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 Earth's highest peaks, including the highest, Mount Everest. More than list of h ...

, in a region stretching from eastern

, northern

, to western

. 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 (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

(11.63 to 5.33 mya) resulted in a sudden speciation event. The species resulting from this event include the

s (''Citrus medica'') of South Asia; the pomelos (''C. maxima'') of

Mainland Southeast Asia Mainland Southeast Asia (historically known as Indochina and the Indochinese Peninsula) 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 th ...

; 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; and the biasong and samuyao (''C. micrantha'') of the

Philippines The Philippines, officially the Republic of the Philippines, is an Archipelagic state, archipelagic country in Southeast Asia. Located in the western Pacific Ocean, it consists of List of islands of the Philippines, 7,641 islands, with a tot ...

. This was followed by the spread of citrus species into

Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...

and Japan in the

Early Pliocene Early may refer to: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a stream in Missouri * Early County, Georgia * Fort Early, Georgia, an early 19th century fort Music * Early B, stage name of Jamaican d ...

(5.33 to 3.6 mya), resulting in the tachibana orange (''C. tachibana''); and beyond the

Wallace Line The Wallace Line or Wallace's Line is a faunal boundary line drawn in 1859 by the British naturalist Alfred Russel Wallace and named by the English biologist Thomas Henry Huxley. It separates the biogeographic realms of Asia and 'Wallacea', a ...

into

Papua New Guinea Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...

and Australia during the

Early Pleistocene The Early Pleistocene is an unofficial epoch (geology), sub-epoch in the international geologic timescale in chronostratigraphy, representing the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently esti ...

(2.5 million to 800,000 years ago), where further speciation events created the Australian limes.

Fossil record

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 preserve ...

leaf from the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Valdarno, Italy is described as †''Citrus meletensis''. In China, fossil leaf specimens of †''Citrus linczangensis'' have been collected from late

Miocene The Miocene ( ) is the first epoch (geology), 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 mea ...

coal-bearing strata of the Bangmai Formation in

province. ''C. linczangensis'' resembles ''C. meletensis'' in having an intramarginal vein, an entire margin, and an articulated and distinctly winged petiole.

Taxonomy

Many cultivated ''Citrus'' species are natural or artificial hybrids of a small number of core ancestral species, including the citron, pomelo, and mandarin. Natural and cultivated citrus hybrids include commercially important fruit such as oranges, grapefruit, lemons, limes, and some tangerines. The multiple hybridisations have made the taxonomy of ''Citrus'' complex. and Supplement Hybrid origins of Citrus

Apart from these core species, Australian limes and the recently discovered mangshanyegan are grown. Kumquats and '' Clymenia'' spp. are now generally considered to belong within the genus ''Citrus''. The false oranges, '' Oxanthera'' from

New Caledonia New Caledonia ( ; ) is a group of islands in the southwest Pacific Ocean, southwest of Vanuatu and east of Australia. Located from Metropolitan France, it forms a Overseas France#Sui generis collectivity, ''sui generis'' collectivity of t ...

, have been transferred to the ''Citrus'' genus on

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

evidence.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), 668–685. A recent taxonomy reincorporates the trifoliate orange (''Poncirus'') into an enlarged ''Citrus'', but recognizes that many botanists still follow Swingle in splitting it off.

History

The earliest introductions of citrus species by human migrations was during the Austronesian expansion (–1500 BCE), where '' Citrus hystrix'', '' Citrus macroptera'', and '' Citrus maxima'' were among the canoe plants carried by Austronesian voyagers eastwards into

and

. 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 (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

, the

Levant The Levant ( ) is the subregion that borders the Eastern Mediterranean, Eastern Mediterranean sea to the west, and forms the core of West Asia and the political term, Middle East, ''Middle East''. In its narrowest sense, which is in use toda ...

and the Mediterranean islands; and a maritime route through the

Arabian Peninsula The Arabian Peninsula (, , or , , ) or Arabia, is a peninsula in West Asia, situated north-east of Africa on the Arabian plate. At , comparable in size to India, the Arabian Peninsula is the largest peninsula in the world. Geographically, the ...

and

Ptolemaic Egypt Ptolemaic is the adjective formed from the name Ptolemy, and may refer to: Pertaining to the Ptolemaic dynasty * Ptolemaic dynasty, the Macedonian Greek dynasty that ruled Egypt founded in 305 BC by Ptolemy I Soter *Ptolemaic Kingdom Pertaining ...

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 (), officially the Republic of Cyprus, is an island country in the eastern Mediterranean Sea. Situated in West Asia, its cultural identity and geopolitical orientation are overwhelmingly Southeast European. Cyprus is the List of isl ...

, dated to around 1200 BCE. Other archaeobotanical evidence includes pollen from

Carthage Carthage was an ancient city in Northern Africa, 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 classic ...

dating back to the 4th century BCE; and carbonized seeds from

Pompeii Pompeii ( ; ) was a city in what is now the municipality of Pompei, near Naples, in the Campania region of Italy. Along with Herculaneum, Stabiae, and Villa Boscoreale, many surrounding villas, the city was buried under of volcanic ash and p ...

dated to around the 3rd to 2nd century BCE. The earliest complete description of the citron was written by

Theophrastus Theophrastus (; ; c. 371 – c. 287 BC) was an ancient Greek Philosophy, philosopher and Natural history, naturalist. A native of Eresos in Lesbos, he was Aristotle's close colleague and successor as head of the Lyceum (classical), Lyceum, the ...

, . Lemons, pomelos, and sour oranges were introduced to the Mediterranean by Arab traders around the 10th century CE. Sweet oranges were brought to Europe by the Genoese and Portuguese from Asia during the 15th to 16th century. Mandarins were not introduced until the 19th century. 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 ''Citrus'' originates from

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

, where it denoted either the

(''C. medica'') or a conifer tree ('' Thuja''). The Latin word is related to the

ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

word for the cedar of Lebanon, (), perhaps from a perceived similarity of the smell of citrus leaves and fruit with that of cedar.

Description

Tree

''Citrus'' 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 Leaf, foliage that remains green and functional throughout the year. This contrasts with deciduous plants, which lose their foliage completely during the winter or dry season. Consisting of many diffe ...

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

with an entire margin. The

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

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 with multiple

carpel Gynoecium (; ; : gynoecia) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more ...

s, 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. This surrounds a variable number of

s, shaped as radial segments. The seeds, if present, develop inside the carpels. The space inside each segment is a locule filled with juice vesicles, or pulp. From the endocarp, string-like "hairs" extend into the locules, which provide nourishment to the fruit as it develops. The genus is commercially important with

cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

s of many species grown for their fruit. Some cultivars have been developed to be easy to peel and seedless, meaning they are parthenocarpic. The fragrance of citrus fruits is conferred by

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 in the rind. The flavonoids include various flavanones and flavones. The carpels are juicy; they contain a high quantity of

citric acid Citric acid is an organic compound with the formula . It is a Transparency and translucency, colorless Weak acid, weak organic acid. It occurs naturally in Citrus, citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, ...

, which with other organic acids including

ascorbic acid Ascorbic acid is an organic compound with formula , originally called hexuronic acid. It is a white solid, but impure samples can appear yellowish. It dissolves freely in water to give mildly acidic solutions. It is a mild reducing agent. Asco ...

(vitamin C) give them their characteristic sharp taste. ''Citrus'' fruits are diverse in size and shape, as well as in color and flavor, reflecting their biochemistry; for instance, grapefruit is made bitter-tasting by a flavanone, naringin. File:Ichangfruit.jpg, Ichang papeda File:Quinotos.jpg, Kumquat, with a

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

inside one of the

s File:Buddhas hand 1.jpg, Buddha's hand File:Citrus australasica red whole.jpg, Red finger lime File:Fortpolyandra.jpg, Clymenia

Cultivation

Most commercial citrus cultivation uses trees produced by

grafting Grafting or graftage is a horticulture, 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 roots ...

the desired fruiting

s onto rootstocks selected for disease resistance and hardiness. The trees are not generally frost hardy. They thrive in a consistently sunny, humid environment with fertile soil and adequate water. The color 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 terms 'ripe' and 'mature' are widely used synonymously, but they mean different things. A mature fruit is one that has completed its growth phase. Ripening is the sequence of changes within the fruit from maturity to the beginning of decay. These changes involve the conversion of starches to sugars, a decrease in acids, softening, and a change in the fruit's color. ''Citrus'' fruits are non- climacteric and respiration slowly declines and the production and release of ethylene is gradual.

Production

According to the UN Food and Agriculture Organization, world production of all citrus fruits in 2016 was 124 million tonnes, 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 that year. According to the

United Nations Conference on Trade and Development UN 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 United Nations General Assembl ...

, 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 for healthy foods. In 2019–20, world production of oranges was estimated to be 47.5 million tonnes, led by Brazil, Mexico, the European Union, and China as the largest producers.

Pests and diseases

Among the diseases of citrus plantations are citrus black spot (a fungus),

citrus canker Citrus canker is a disease affecting ''Citrus'' species caused by the bacterium '' Xanthomonas citri''. Infection causes lesions on the leaves, stems, and fruit of citrus trees, including lime, oranges, and grapefruit. While not harmful to huma ...

(a bacterium), citrus greening (a bacterium, spread by an insect pest), and sweet orange scab (a fungus, ''Elsinöe australis''). Citrus plants are liable to infestation by ectoparasites which act as vectors to plant diseases: for example, aphids transmit the damaging citrus tristeza virus, while the aphid-like Asian citrus psyllid can carry the bacterium which causes the serious citrus greening disease. This threatens production in Florida, California, and worldwide. Citrus groves are attacked by parasitic

Nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

s including citrus ('' Tylenchulus semipenetrans'') and sheath nematodes ('' Hemicycliophora'' spp.). File:Citrus Black Spot on Valencia orange (detail).jpg, Citrus black spot on a Valencia orange File:CTV Leaf Chlorosis.jpg, Chlorosis caused by Citrus tristeza virus File:Citrus canker on fruit.jpg,

Citrus canker Citrus canker is a disease affecting ''Citrus'' species caused by the bacterium '' Xanthomonas citri''. Infection causes lesions on the leaves, stems, and fruit of citrus trees, including lime, oranges, and grapefruit. While not harmful to huma ...

, caused by the gammaproteobacterium ''Xanthomonas axonopodis'' File:Asian Citrus Psyllid adult (detail).jpg, Asian citrus psyllid, vector of citrus greening disease File:Huanglongbing (cropped).jpg, Citrus greening disease on mandarin orange File:Life stages of citrus nematode.svg, Life stages of the citrus

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

,'' Tylenchulus semipenetrans''

Deficiency diseases

Citrus plants can develop the deficiency condition chlorosis, characterized by yellowing leaves.Online at SumoGardener The condition is often caused by an excessively high pH (

alkaline soil Alkali, or alkaline, soils are clay soils with high Soil pH, pH (greater than 8.5), a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable ...

), which prevents the plant from absorbing nutrients such as iron,

magnesium Magnesium is a chemical element; it has Symbol (chemistry), 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 ...

, and

zinc Zinc is a chemical element; it has symbol Zn and atomic number 30. It 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 periodic tabl ...

needed to produce

chlorophyll Chlorophyll 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 allows plants to absorb energy ...

Effects on humans

Some ''Citrus'' species contain significant amounts of furanocoumarins. In humans, some of these act as strong photosensitizers when applied topically to the skin, while others interact with medications when taken orally in the grapefruit juice effect. Due to the photosensitizing effects of certain furanocoumarins, some ''Citrus'' species cause

phytophotodermatitis Phytophotodermatitis, also known as berloque dermatitis,, margarita photodermatitis,, lime disease or lime phytodermatitis is a cutaneous phototoxic inflammatory reaction resulting from contact with a light-sensitizing botanical agent (such as ...

, a potentially severe skin inflammation resulting from contact with a light-sensitizing botanical agent followed by exposure to

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

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 Psoralen (also called psoralene) is the parent compound in a family of naturally occurring organic compounds known as the linear furanocoumarins. It is structurally related to coumarin by the addition of a fused furan ring, and may be considered a ...

. This claim has been confirmed for lime and bergamot. In particular,

bergamot essential oil Bergamot essential oil is a cold-pressed essential oil produced by cells inside the rind of a bergamot orange fruit. It is a common flavouring and top note in perfumes. The scent of bergamot essential oil is similar to a sweet light orange pe ...

has a higher concentration of bergapten (3–3.6 g/kg) than any other ''Citrus''-based essential oil. A

systematic review A systematic review is a scholarly synthesis of the evidence on a clearly presented topic using critical methods to identify, define and assess research on the topic. A systematic review extracts and interprets data from published studies on ...

indicates that citrus fruit consumption is associated with a 10% reduction of risk for developing breast cancer.

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. Lemonade is a popular beverage prepared by diluting the juice and adding sugar. Lemon juice is mixed in salad dressings and squeezed over fruit salad to stop it from turning brown: its acidity suppresses

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

by polyphenol oxidase enzymes. A variety of flavors can be derived from different parts and treatments of citrus fruits. The colorful outer skin of some citrus fruits, known as zest, is used as a flavoring in cooking. The whole of the bitter orange (and sometimes other citrus fruits) including the peel with its

essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...

s is cooked with sugar to make marmalade. File:Fried chicken legs!.JPG, Fried chicken garnished with lemon and onion File:Calamansi (sliced) - Philippines.jpg, Calamansi, ubiquitous in Philippine condiments File:Pomeranzen.jpg, Bitter oranges (''Citrus × aurantium'') are used for marmalade. File:Bottled Sunshine.jpg, Marmalade, with orange peel File:Lemonade 2.jpg, Lemonade

As ornamental plants

By the 17th century, orangeries were added to great houses in Europe, both to enable the fruit to be grown locally and for prestige, as seen in the Versailles Orangerie. Some modern hobbyists grow dwarf citrus in containers or greenhouses in areas where the weather is too cold to grow it outdoors; '' Citrofortunella'' hybrids have good cold resistance.

In art and culture

Lemons appear in paintings, pop art, and novels. A wall painting in the tomb of Nakht in 15th century BC Egypt depicts a woman in a festival, holding a lemon. In the 17th century, Giovanna Garzoni painted a ''Still Life with Bowl of Citrons'', the fruits still attached to leafy flowering twigs, with a wasp on one of the fruits. The impressionist Edouard Manet depicted a lemon on a pewter plate. In modern art, Arshile Gorky painted ''Still Life with Lemons'' in the 1930s. Citrus fruits "were the clear status symbols of the nobility in the ancient Mediterranean", according to the Paleoethnobotany, paleoethnobotanist Dafna Langgut. In Louisa May Alcott's 1868 novel ''Little Women'', the character Amy March states that "It's nothing but limes now, for everyone is sucking them in their desks in schooltime, and trading them off for pencils, bead rings, paper dolls, or something else… If one girl likes another, she gives her a lime; if she’s mad with her, she eats one before her face, and doesn’t offer even a suck."

References

External links

Citrus Research and Education Center
of Institute of Food and Agricultural Sciences, IFAS {{Authority control Citrus, Cocktail garnishes Garden plants Lists of foods, Citrus fruits Lists of plants Ornamental trees Aurantioideae genera Taxa named by Carl Linnaeus