Trifoliate orange

The trifoliate orange is recognizable by the large {{convert|3–5|cm|abbr=on}} thorns on the shoots, and its deciduous leaves with three (or rarely, five) leaflets, typically with the middle leaflet {{convert|3–5|cm|abbr=on}} long, and the two side leaflets {{convert|2–3|cm|abbr=on}} long. The flowers are white, with pink stamens, {{convert|3–5|cm|abbr=on}} in diameter, larger than those of true citrus but otherwise closely resembling them, except that the scent is much less pronounced than with true citrus. As with true citrus, the leaves give off a spicy smell when crushed.

The fruits are green, ripening to yellow, and {{convert|3–4|cm|abbr=on}} in diameter similar in size to a lime and resembling a small orange, but with a finely downy surface and having a fuzzy texture similar to a peach. The fruits also have distinctive smell from other citrus varieties and often contain a high concentration of seeds.

File:Poncirus trifoliata0.jpg|Flower

File:Poncirus trifoliata R.H (3).JPG|Leaves and thorns

File:20130817Citrus trifoliata3.jpg|Green fruits

File:Poncirus trifoliata (cut).JPG|Bisected fruit

The cultivar 'Flying Dragon' is dwarfed in size, has highly twisted, contorted stems, and has even stronger thorns than the type. It makes an excellent barrier hedge due to its density and strong curved thorns. Such hedges have been grown for over 50 years at Oklahoma State University in Stillwater, and are highly student-proof.{{cite web |url=http://www.uaex.uada.edu/yard-garden/resource-library/plant-week/hardy-orange-2-9-07.aspx |title=Plant of the Week. Hardy Orange or Trifoliate Orange. Latin: Poncirus trifoliat |publisher=University of Arkansas Division of Agriculture |first=Gerald |last=Klingaman}} The plant is also highly deer-resistant.{{cite web|url=http://www.eattheweeds.com/hardy-orange/|title=Hardy Orange |last=Hardy |first=Green Deane |date=December 2012 }} In central London, mature specimens of the trifoliate orange can be seen in the gardens of St Paul's Cathedral.{{cite web |title=The Orange Trees of St. Paul's Cathedral |url=https://www.homecitrusgrowers.co.uk/wheretoseePT/stpaulscathedral.html |website=Home Citrus Growers |access-date=28 February 2025}}

Trifoliate orange and various of its hybrids with other Citrus are widely used as citrus rootstock, which are valued for their resistance to cold, the tristeza virus, and the oomycete Phytophthora parasitica (root rot).{{cite web |title=Notice to Fruit Growers and Nurserymen Related to the Naming and Release of the US-942 Citrus Rootstock |url=http://www.southeastagnet.com/documents/US-942-signed-release-notice.pdf |publisher=Agricultural Research Service, USDA|date=22 October 2010 |pages=1–2 |access-date=23 October 2017}}

Recent studies have revealed that the trifoliate orange contains auraptene at a high concentration, which is one of the functional components having immunity against citrus tristeza virus (CTV).{{cite web|url=http://www.naro.affrc.go.jp/project/results/laboratory/fruit/2006/fruit06-11.html |title=Karatachi no kankitsu torisuteza wīrusu teikōsei to rensa suru DNA mākā |trans-title=PCR Primers for Marker Assisted Backcrossing to Introduce a CTV Resistance Gene from Poncirus trifoliata (L.) Raf. into Citrus |author1=Ohta, Satoshi |author2=Endo, Tomoko |author3=Shimada, Takehiko |author4=Fujii, Hiroshi |others=Shimizu, Tokuro; Kuniga, Takeshi; Yoshioka, Terutaka; Nesumi, Hirohisa; Yoshida, Toshio; Omura, Mitsuo (Shizuoka University) |publisher=Japanese Society for Horticultural Science |volume=80 |number=3 |pages=295–307 |year=2011 |access-date=23 October 2017}}

Trifoliate orange fruits are very bitter, due in part to their poncirin content. Most people consider them inedible fresh, but they can be made into marmalade. When dried and powdered, they can be used as a condiment.{{cite web|url=https://specialtyproduce.com/produce/Japanese_Bitter_Oranges_10119.php |title=Japanese Bitter Oranges | publisher=Specialty Produce | access-date=22 October 2024}}

The fruits of the trifoliate orange are widely used in medical traditions of East Asia as a treatment for allergic inflammation.{{citation |pmid=17662711 |author1=Zhou, H.Y. |author2=Shin, E.M. |author3=Guo, L.Y. |author4=Zou, L.B. |author5=Xu, G.H. |author6=Lee, S.-H. |author7=Ze, K.R. |author8=Kim, E.-K. |author9=Kang, S.S. |author10=Kim, Y.S. |title=Anti-inflammatory activity of 21(alpha, beta)-methylmelianodiols, novel compounds from Poncirus trifoliata Rafinesque |journal=European Journal of Pharmacology |volume=572 |issue=2–3 |pages=239–248 |year=2007 |doi=10.1016/j.ejphar.2007.07.005}}

The species has been planted as a security barrier due to its quick, dense growth and sharp thorns.{{cite book |last=Manaugh |first=Geoff |date=2016 |title=A Burglar's Guide to the City |location=New York |publisher=Farrar, Straus and Giroux |pages=210-211 |isbn=978-0374117269}}

The trifoliate orange was considered a member of the genus Citrus until Walter Swingle (1871 – 1952) moved it in 1943 to its own separate genus, Poncirus, based on its deciduous trifoliate leaves differing from other Citrus and as part of a larger reclassification that split the historical Citrus into seven genera. More recently, David Mabberley and Dianxiang Zhang reunited all of Swingle's novel genera back into Citrus in 2008.{{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 }} Early phylogenetic analysis of trifoliate orange plastids nested Poncirus within the citrus, consistent with a single genus,{{cite journal |title=Citrus phylogeny and genetic origin of important species as investigated by molecular markers |last1=Nicolosi |first1=E. |last2=Deng |first2=Z. N. |last3=Gentile |first3=A. |last4= La Malfa |first4=S. |last5=Continella |first5=G. |last6=Tribulato |first6=E. |journal=Theoretical and Applied Genetics |volume=100 |issue=8 |pages=1155–1166 |date=2000 |doi=10.1007/s001220051419 |s2cid=24057066}}{{cite journal |doi=10.1078/1439-6092-00058 |title=What is Citrus? Taxonomic implications from a study of cp-DNA evolution in the tribe Citreae (Rutaceae subfamily Aurantioideae) |journal=Organisms Diversity & Evolution |last1=de Araújo |first1=Edson Freitas |last2=Queiroza |first2=Luciano Paganuccide |last3=Machado |first3=Marcos Antônio |date=2003 |volume= 1 |pages=55–62|doi-access=free |bibcode=2003ODivE...3...55D }}{{cite journal |last1=Bayer |first1=Randall J. |last2=Mabberly |first2=David J. |last3=Morton |first3=Cynthia |last4=Miller |first4=Cathy H. |last5=Sharma |first5=Ish K. |last6=Pfiel |first6=Bernard E. |last7=Rich |first7=Sarah |last8=Hitchcock |first8=Roberta |last9=Sykes |first9=Steve |date=2009 |title=A molecular phylogeny of the orange subfamily (Rutaceae: Aurantioideae) using nine cpDNA sequences |journal=American Journal of Botany |volume=96 |issue=3 |pages=668–685 |doi=10.3732/ajb.0800341 |pmid=21628223|s2cid=29306927 }}{{cite journal |title=A nuclear phylogenetic analysis: SNPs, indels and SSRs deliver new insights into the relationships in the 'true citrus fruit trees' group (Citrinae, Rutaceae) and the origin of cultivated species |last1=Garcia-Lor |first1=Andres |last2=Curk |first2=Franck |last3=Snoussi-Trifa |first3=Hager |last4=Morillon |first4=Raphael |last5=Ancillo |first5=Gema |last6=Luro |first6=François |last7=Navarro |first7=Luis |last8=Ollitrault |first8=Patrick |journal=Annals of Botany |volume=111 |issue=1 |pages=1–19 |date=2011 |doi=10.1093/aob/mcs227 |pmid=23104641 |pmc=3523644}} but the sequencing of the nuclear genome by Wu, et al. showed its genome to be most divergent, different enough to justify retention of Poncirus as a separate genus.{{cite journal |title=Genomics of the origin and evolution of Citrus |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. Jr. |last17=Rokhsar |first17=Daniel |last18=Talon |first18=Manuel |journal=Nature |date=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 To explain the conflict between the plastid and nuclear genomic analysis, it was speculated that the trifoliate orange is likely either the progeny of an ancient hybridization between a core citrus and an unidentified more distant relative, or at some time in its history it acquired an introgressed cpDNA genome from another species.{{cite book |chapter=The origin of citrus |last1=Talon |first1=Manuel |last2=Wu |first2=Guohong Albert |last3=Gmitter |first3=Frederick G. |last4=Rokhsar |first4=Daniel S |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=9–31 |isbn=978-0-12-812163-4|doi=10.1016/C2016-0-02375-6|s2cid=87258420 }} Ollitrault, Curk and Krueger indicate that the majority of data are consistent with the enlarged Citrus that includes the trifoliate orange, though they recognize that many botanists still follow Swingle.

A second species of trifoliate orange native to Yunnan (China) has been reported and named Poncirus polyandra.{{cite journal |title=A nuclear phylogenetic analysis: SNPs, indels and SSRs deliver new insights into the relationships in the 'true citrus fruit trees' group (Citrinae, Rutaceae) and the origin of cultivated species |last1=Garcia-Lor |first1=Andres |last2=Curk |first2=Franck |last3=Snoussi-Trifa |first3=Hager |last4=Morillon |first4=Raphael |last5=Ancillo |first5=Gema |last6=Luro |first6=François |last7=Navarro |first7=Luis |last8=Ollitrault |first8=Patrick |journal=Annals of Botany |volume=111 |pages=1–19 |year=2011 |issue=1 |doi=10.1093/aob/mcs227|pmc=3523644 |pmid=23104641}} Were Poncirus to be subsumed into Citrus, where C. polyandra is unavailable, the name Citrus polytrifolia has been suggested.{{cite web|title=Citrus polytrifolia|website=NCBI Taxonomy Browser|url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi|access-date=2 February 2021}} Zhang and Mabberley concluded this Yunnan cultivar is likely a hybrid between the trifoliate orange and another Citrus, but recent genomic analysis of P. polyandra showed low levels of heterozygosity,{{cite journal|title=A chromosome-scale reference genome of trifoliate orange (Poncirus trifoliata) provides insights into disease resistance, cold tolerance and genome evolution in Citrus |first1=Ze |last1=Peng |first2=Jessen V. |last2=Bredeson |first3=Guohong A. |last3=Wu |first4=Shengqiang |last4=Shu |first5=Nidhi |last5=Rawat |first6=Dongliang |last6=Du |first7=Saroj |last7=Parajuli |first8=Qibin |last8=Yu |first9=Qian |last9=You |first10=Daniel S. |last10=Rokhsar |first11=Frederick G. Jr |last11=Gmitter |first12=Zhanao |last12=Deng |journal=The Plant Journal |volume=104 |pages=1215–1232 |year=2020 |issue=5 |doi=10.1111/tpj.14993|pmid=32985030 |pmc=7756384 |doi-access=free }} the opposite of what one would expect for a hybrid. This analysis dated its divergence from P. trifoliata about 2.82 million years ago.

The trifoliate orange does not naturally interbreed with core Citrus taxa due to different flowering times,{{cite journal |title=New universal mitochondrial PCR markers reveal new information on maternal citrus phylogeny |doi=10.1007/s11295-010-0314-x |volume=7 |journal=Tree Genetics & Genomes |pages=49–61 |year=2011 |last1=Froelicher |first1=Yann |last2=Mouhaya |first2=Wafa |last3=Bassene |first3=Jean-Baptiste |last4=Costantino |first4=Gilles |last5=Kamiri |first5=Mourad |last6=Luro |first6=Francois |last7=Morillo |first7=Raphael |last8=Ollitrault |first8=Patrick|s2cid=32371305 |url=http://agritrop.cirad.fr/558353/|url-access=subscription }} but hybrids have been produced artificially between the trifoliate orange and other citrus. In the Swingle system, where the trifoliate orange is placed in Poncirus, a hybrid genus name has been coined for these intra-generic crosses, "× Citroncirus". The most notable of these are the citrange, a cross between the trifoliate and sweet oranges, and the citrumelo, a hybrid of trifoliate orange and 'Duncan' grapefruit. Placing the trifoliate orange in Citrus would mean these hybrids would no longer be intergeneric, but instead hybrids within Citrus. Genomic analysis of a number of these hybrids showed them all to derive from P. trifoliata and not P. polyandra.

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Category:Fruits originating in East Asia