Editing Citrus (section)

== 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 (plant)|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''<ref name="citrus taxonomy">{{cite book |chapter=''Citrus'' taxonomy |last1=Ollitrault |first1=Patrick |last2=Curk |first2=Franck |last3=Krueger |first3=Robert |title=The Citrus Genus |editor-last1=Talon |editor-first1=Manuel |editor-last2=Caruso |editor-first2=Marco |editor-last3=Gmitter |editor-first3=Frederick G. Jr. |publisher=Elsevier |date=2020 |pages=57–81 |isbn=978-0-12-812163-4 |chapter-url= https://books.google.com/books?id=2wo4swEACAAJ&pg=PA57 |doi=10.1016/B978-0-12-812163-4.00004-8|s2cid=242819146 }}</ref> ''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]]s.<ref>{{Cite web|url=http://mbe.oxfordjournals.org/content/early/2015/04/05/molbev.msv082.full.pdf+html|title=A phylogenetic analysis of 34 chloroplast genomes elucidates the relationships between wild and domestic species within the genus Citrus|date=31 January 2016|access-date=6 May 2021|archive-date=31 January 2016|archive-url=https://web.archive.org/web/20160131222305/http://mbe.oxfordjournals.org/content/early/2015/04/05/molbev.msv082.full.pdf+html|url-status=bot: unknown}}</ref> A DNA study published in ''[[Nature (journal)|Nature]]'' in 2018 concludes that the genus ''Citrus'' evolved in the foothills of the [[Himalaya]]s, in the area of [[Assam]] (India), western [[Yunnan]] (China), and northern [[Myanmar]].<ref>{{cite web |last=Briggs |first=Helen |date=8 February 2018 |title=DNA Story of when life first gave us lemons |work=BBC News |url=https://www.bbc.com/news/science-environment-42960445 |access-date=19 July 2022}}</ref>

[[File:Map of inferred original wild ranges of the main Citrus cultivars, and selected relevant wild taxa (Fuller et al., 2017).png|thumb|left|upright=1.2|Map of inferred original wild ranges of the main ''Citrus'' cultivars, and selected relevant wild taxa<ref name="fuller"/>]]

The three ancestral species in the genus ''Citrus'' associated with modern ''Citrus'' cultivars are the [[mandarin orange]], [[pomelo]], and [[citron]]. Almost all of the common commercially important citrus fruits (sweet oranges, [[lemon]]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.<ref name="Wu"/><ref>{{cite journal |title=A genealogy of the citrus family |first1=Riccardo |last1=Velasco |first2=Concetta |last2=Licciardello |journal=Nature Biotechnology |volume=32 |issue=7 |pages=640–642 |doi=10.1038/nbt.2954 |pmid=25004231 |year=2014 |s2cid=9357494 |doi-access=free}}</ref><ref>{{cite book |last1=Inglese |first1=Paolo |title=Oxford Research Encyclopedia of Environmental Science |last2=Sortino |first2=Giuseppe |chapter=Citrus History, Taxonomy, Breeding, and Fruit Quality |date=2019 |doi=10.1093/acrefore/9780199389414.013.221 |isbn=9780199389414}}</ref>

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]], leaving much uncertainty about when and where domestication first happened.<ref name="Wu">{{cite journal | last1=Wu | first1=Guohong Albert | last2=Terol | first2=Javier | last3=Ibanez | first3=Victoria | last4=López-García | first4=Antonio | last5=Pérez-Román | first5=Estela | last6=Borredá | first6=Carles | last7=Domingo | first7=Concha | last8=Tadeo | first8=Francisco R. | last9=Carbonell-Caballero | first9=Jose | last10=Alonso | first10=Roberto | last11=Curk | first11=Franck | last12=Du | first12=Dongliang | last13=Ollitrault | first13=Patrick | last14=Roose | first14=Mikeal L. | last15=Dopazo | first15=Joaquin | last16=Gmitter | first16=Frederick G. | last17=Rokhsar | first17=Daniel S. | last18=Talon | first18=Manuel |display-authors=5 | title=Genomics of the origin and evolution of Citrus | journal=Nature | volume=554 | issue=7692 | year=2018 | pages=311–316 | doi=10.1038/nature25447 | doi-access=free | pmid=29414943 | bibcode=2018Natur.554..311W | hdl=20.500.11939/5741 | hdl-access=free}}</ref> 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]], in a region stretching from eastern [[Assam]], northern [[Myanmar]], to western [[Yunnan]]. It diverged from a common ancestor with ''[[Trifoliate orange|Poncirus trifoliata]]''. A change in climate conditions during the [[Late Miocene]] (11.63 to 5.33 [[million years ago|mya]]) resulted in a [[Evolutionary radiation|sudden speciation event]]. The species resulting from this event include the [[citron]]s (''Citrus&nbsp;medica'') of South Asia; the [[pomelo]]s (''C.&nbsp;maxima'') of [[Mainland Southeast Asia]]; the [[mandarin orange|mandarin]]s (''C.&nbsp;reticulata''), [[kumquat]]s (''C.&nbsp;japonica''), [[mangshanyegan]] (''C.&nbsp;mangshanensis''), and [[ichang papeda]]s (''C.&nbsp;cavaleriei'') of southeastern China; the [[kaffir lime]]s (''C.&nbsp;hystrix'') of [[Island Southeast Asia]]; and the [[biasong]] and [[samuyao]] (''C.&nbsp;micrantha'') of the [[Philippines]].<ref name="Wu"/><ref name="fuller"/> 

This was followed by the spread of citrus species into [[Taiwan]] and Japan in the [[Early Pliocene]] (5.33 to 3.6 [[million years ago|mya]]), resulting in the [[tachibana orange]] (''C.&nbsp;tachibana''); and beyond the [[Wallace Line]] into [[Papua New Guinea]] and Australia during the [[Early Pleistocene]] (2.5&nbsp;million to 800,000 years ago), where further speciation events created the [[Australian lime]]s.<ref name="Wu"/><ref name="fuller">{{cite book |first1=Dorian Q. |last1=Fuller |first2=Cristina |last2=Castillo |first3=Eleanor |last3=Kingwell-Banham |first4=Ling |last4=Qin |first5=Alison |last5=Weisskopf|editor1-first=Véronique |editor1-last=Zech-Matterne |editor2-first=Girolamo|editor2-last=Fiorentino |title=AGRUMED: Archaeology and history of citrus fruit in the Mediterranean |chapter=Charred pomelo peel, historical linguistics and other tree crops: approaches to framing the historical context of early Citrus cultivation in East, South and Southeast Asia |publisher=Publications du Centre Jean Bérard |year=2017 |pages=29–48 |isbn=9782918887775 |doi=10.4000/books.pcjb.2107 |url=https://hal.archives-ouvertes.fr/hal-03501166/file/2017-Ruas-etal-Citrus.pdf |chapter-url =https://books.openedition.org/pcjb/2173?lang=en}}</ref>

=== Fossil record ===

A [[fossil]] leaf from the [[Pliocene]] of [[Valdarno]], Italy is described as †''Citrus meletensis''.<ref>Citrus meletensis (Rutaceae), a new species from the Pliocene of Valdarno (Italy). Fischer, T.C. & Butzmann, Plant Systematics and Evolution – March 1998, Volume 210, Issue 1, pp 51–55. doi:10.1007/BF00984727</ref>
In China, fossil leaf specimens of †''Citrus linczangensis'' have been collected from late [[Miocene]] coal-bearing strata of the Bangmai Formation in [[Yunnan]] province. ''C. linczangensis'' resembles ''C. meletensis'' in having an intramarginal vein, an entire margin, and an articulated and distinctly winged [[Petiole (botany)|petiole]].<ref>{{cite journal |last1=Xie |first1=Sanping Xie |last2=Manchester |first2=Steven R. |last3=Liu |first3=Kenan |last4=Sun |first4=Bainian |title=''Citrus linczangensis'' sp. n., a Leaf Fossil of Rutaceae from the Late Miocene of Yunnan, China |journal=International Journal of Plant Sciences |date=October 2013 |volume=174 |issue=8 |pages=1201–1207| doi=10.1086/671796 |bibcode=2013IJPlS.174.1201X }}</ref>

=== Taxonomy ===

{{Main|Citrus taxonomy}}

Many cultivated ''Citrus'' species are [[hybrid (biology)|natural]] or [[Hybrid speciation|artificial hybrids]] of a small number of core ancestral species, including the citron, pomelo, and mandarin. Natural and cultivated [[citrus hybrid]]s include commercially important fruit such as oranges, [[grapefruit]], lemons, limes, and some [[tangerine]]s. The multiple hybridisations have made the taxonomy of ''Citrus'' complex.<ref>{{Cite book |last1=Klein |first1=Joshua D. |volume=2 |pages=199–214 |doi=10.1007/978-94-017-9276-9_10 |series=Medicinal and Aromatic Plants of the World |year=2014 |title=Medicinal and Aromatic Plants of the Middle-East |isbn=978-94-017-9275-2 |chapter=Citron Cultivation, Production and Uses in the Mediterranean Region}}</ref><ref name="Wu Terol Ibanez 2018">{{cite journal |last1=Wu |first1=Guohong Albert |last2=Terol |first2=Javier |last3=Ibanez |first3=Victoria |last4=López-García |first4=Antonio |last5=Pérez-Román |first5=Estela |last6=Borredá |first6=Carles |last7=Domingo |first7=Concha |last8=Tadeo |first8=Francisco R. |last9=Carbonell-Caballero |first9=Jose |last10=Alonso |first10=Roberto |last11=Curk |first11=Franck |last12=Du |first12=Dongliang |last13=Ollitrault |first13=Patrick |last14=Roose |first14=Mikeal L. Roose |last15=Dopazo |first15=Joaquin |last16=Gmitter Jr |first16=Frederick G. |last17=Rokhsar |first17=Daniel |last18=Talon |first18=Manuel |display-authors=6 |title=Genomics of the origin and evolution of ''Citrus'' |journal=[[Nature (journal)|Nature]] |year=2018 |volume=554 |issue=7692 |pages=311–316 |doi=10.1038/nature25447 |pmid=29414943 |bibcode=2018Natur.554..311W |doi-access=free |hdl=20.500.11939/5741 |hdl-access=free}} and Supplement</ref>

[[File:Hybrid origins of Citrus.svg|thumb|center|upright=3|Many ''Citrus'' species are [[Hybrid (biology)|hybrids]] of [[citron]], [[Mandarin orange|mandarin]] and [[pomelo]].<ref name="Wu Terol Ibanez 2018"/>]]

Apart from these core species, [[Australian lime]]s and the recently discovered [[mangshanyegan]] are grown. [[Kumquat]]s and ''[[Clymenia (plant)|Clymenia]]'' spp. are now generally considered to belong within the genus ''Citrus''.<ref name="AGLthesis">{{cite thesis |last=García Lor |first=Andrés |title=Organización de la diversidad genética de los cítricos |language=Spanish |trans-title=Organisation of the genetic diversity of the citruses |year=2013 |url=https://riunet.upv.es/bitstream/handle/10251/31518/Versión3.Tesis%20Andrés%20García-Lor.pdf |page=79}}</ref> The false oranges, ''[[Oxanthera]]'' from [[New Caledonia]], have been transferred to the ''Citrus'' genus on [[Phylogenetics|phylogenetic]] evidence.<ref name=bayer>Bayer, R. J., et al. (2009). [https://web.archive.org/web/20150331210237/http://www.amjbot.org/content/96/3/668.full A molecular phylogeny of the orange subfamily (Rutaceae: Aurantioideae) using nine cpDNA sequences.] ''American Journal of Botany'' 96(3), 668–685.</ref><ref name="POWO_35867-1">{{cite web |title=''Oxanthera'' Montrouz |work=Plants of the World Online |publisher=[[Royal Botanic Gardens, Kew]] |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:35867-1 |access-date=10 September 2021}}</ref> A recent taxonomy reincorporates the trifoliate orange (''Poncirus'') into an enlarged ''Citrus'', but recognizes that many botanists still follow Swingle in splitting it off.<ref name="citrus taxonomy" />