The trifoliate orange, ''Citrus trifoliata'' or ''Poncirus trifoliata'', is a member of the family
Rutaceae. Whether the trifoliate oranges should be considered to belong to their own genus, ''Poncirus'', or be included in the genus ''Citrus'' is debated. The species is unusual among citrus for having
deciduous
In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, aft ...
,
compound leaves
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
and pubescent (downy) fruit.
It is native to northern
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 exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
and
Korea
Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic o ...
, and is also known as the Japanese bitter-orange,
hardy orange or Chinese bitter orange.
The plant is a fairly
cold-hardy citrus
Cold-hardy citrus is citrus with increased frost tolerance and which may be cultivated far beyond traditional citrus growing regions. Citrus species and citrus hybrids typically described as cold-hardy generally display an ability to withstand win ...
(
USDA zone 6) and will tolerate moderate frost and snow, making a large
shrub
A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...
or small tree tall. Because of its relative hardiness, citrus grafted onto ''Citrus trifoliata'' are usually hardier than when grown on their own roots.
Description
The trifoliate orange is recognizable by the large thorns on the shoots, and its deciduous leaves with three (or rarely, five) leaflets, typically with the middle leaflet long, and the two side leaflets long. The flowers are white, with pink stamens, 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 in diameter similar in size to a
lime
Lime commonly 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 may also refer to:
Botany ...
and resembling a small
orange, but with a finely downy surface and having a fuzzy texture similar to a
peach
The peach (''Prunus persica'') is a deciduous tree first domesticated and cultivated in Zhejiang province of Eastern China. It bears edible juicy fruits with various characteristics, most called peaches and others (the glossy-skinned, non-fu ...
. The fruits also have distinctive smell from other citrus varieties and often contain a high concentration of seeds.
Image:Poncirus trifoliata0.jpg, Flower
Image:Poncirus trifoliata R.H (3).JPG, Leaves and thorns
File:20130817Citrus trifoliata3.jpg, Green fruits
File:Unknown fruit Bury St Edmunds.jpg, Bisected fruit
Uses
Cultivation
The
cultivar
A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
'Flying Dragon' is dwarfed in size and has highly twisted, contorted stems. It makes an excellent barrier
hedge
A hedge or hedgerow is a line of closely spaced shrubs and sometimes trees, planted and trained to form a barrier or to mark the boundary of an area, such as between neighbouring properties. Hedges that are used to separate a road from adjoini ...
due to its density and strong curved thorns. Such hedges have been grown for over 50 years at
Oklahoma State University
Oklahoma (; Choctaw: ; chr, ᎣᎧᎳᎰᎹ, ''Okalahoma'' ) is a state in the South Central region of the United States, bordered by Texas on the south and west, Kansas on the north, Missouri on the northeast, Arkansas on the east, New ...
in
Stillwater, and are highly student-proof.
The plant is also highly deer-resistant.
In
central London
Central London is the innermost part of London, in England, spanning several boroughs. Over time, a number of definitions have been used to define the scope of Central London for statistics, urban planning and local government. Its characteris ...
, mature specimens of the trifoliate orange can be seen in the gardens of
St Paul's Cathedral
St Paul's Cathedral is an Anglican cathedral in London and is the seat of the Bishop of London. The cathedral serves as the mother church of the Diocese of London. It is on Ludgate Hill at the highest point of the City of London and is a Grad ...
.
Trifoliate orange and various hybrids of this plant are widely used as
citrus rootstock Citrus rootstock are plants used as rootstock for citrus plants. A rootstock plant must be compatible for scion grafting, and resistant to common threats, such as drought, frost, and common citrus diseases.
Principal rootstocks
Five types of rootst ...
.
Recent studies have revealed that the trifoliate orange contains
auraptene
Auraptene is a natural bioactive monoterpene coumarin ether. It was first isolated from members of the genus ''Citrus
''Citrus'' is a genus of flowering plant, flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produc ...
at a high concentration, which is one of the functional components having immunity against
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 ...
(CTV).
As food
The fruits are very bitter, due in part to their
poncirin
Poncirin is the 7-O-neohesperidoside of isosakuranetin. Poncirin can be extracted from trifoliate orange
The trifoliate orange, ''Citrus trifoliata'' or ''Poncirus trifoliata'', is a member of the family Rutaceae. Whether the trifoliate oranges ...
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.
]
Medicine
Traditional medicine
The fruits of the trifoliate orange are widely used in medical traditions of East Asia as a treatment for allergic inflammation.
Taxonomy
The trifoliate orange was historically considered a member of the genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Citrus'' until Walter Swingle
Walter Tennyson Swingle (January 8, 1871 – January 19, 1952) was an American agricultural botanist who contributed greatly to the classification and taxonomy of citrus.
Biography
Swingle was born in Canaan, Pennsylvania, and moved with his f ...
moved it to its own novel genus, ''Poncirus
The trifoliate orange, ''Citrus trifoliata'' or ''Poncirus trifoliata'', is a member of the family Rutaceae. Whether the trifoliate oranges should be considered to belong to their own genus, ''Poncirus'', or be included in the genus ''Citrus'' is ...
'', based on its deciduous trifoliate leaves differing from other ''Citrus'', as part of a larger reclassification that split the historical ''Citrus'' into seven genera. However, David Mabberley
Professor David John Mabberley , (born May 1948) is a British-born botanist, educator and writer. Among his varied scientific interests is the taxonomy of tropical plants, especially trees of the families Labiatae, Meliaceae and Rutaceae. He i ...
and Dianxiang Zhang reunited all of Swingle's novel genera back into ''Citrus''. Early phylogenetic analysis of trifoliate orange plastid
The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. They are considered to be intracellular endosy ...
s nested ''Poncirus'' within the citrus, consistent with a single genus, 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.[ 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
Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Intr ...
cpDNA genome from another species. 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
Yunnan , () is a landlocked Provinces of China, province in Southwest China, 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 ...
(China) has been reported and named ''Poncirus polyandra''. Were ''Poncirus'' to be subsumed into ''Citrus'', where ''C. polyandra'' is unavailable, the name ''Citrus polytrifolia'' has been suggested. 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
Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism.
Mo ...
, 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, 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
The citrange (a portmanteau of ''citrus'' and ''orange'') 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 d ...
, a cross between the trifoliate and sweet oranges, and the citrumelo, a hybrid of trifoliate orange and 'Duncan' grapefruit
The grapefruit (''Citrus'' × ''paradisi'') is a subtropical citrus tree known for its relatively large, sour to semi-sweet, somewhat bitter fruit. The interior flesh is segmented and varies in color from pale yellow to dark pink.
Grapefruit is ...
. 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''.
References
{{Taxonbar, from=Q859433
Citrus
Flora of China
Flora of Korea
Garden plants of Asia
Medicinal plants
Oranges (fruit)
Fruits originating in East Asia