The trifoliate orange, ''Citrus trifoliata'' ( syn. ''Poncirus trifoliata''), is a member of the family

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

. 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 Leaf, leaves, usually in the autumn; to the shedding of petals, aft ...

, compound leaves 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. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

and

Korea Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...

, and is also known as the Japanese bitter-orange (karatachi), hardy orange or Chinese bitter orange. The plant is a fairly cold-hardy citrus (

USDA zone A hardiness zone is a geographic area defined as having a certain average annual minimum temperature, a factor relevant to the survival of many plants. In some systems other statistics are included in the calculations. The original and most widely ...

6) and will tolerate moderate frost and snow, making a large

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 ...

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 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 Agriculture, cultivated in China. It bears edible juicy fruits with various characteristics, most called peaches and the glossy-skinned, non-fuzzy varieties called necta ...

. 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

Uses

Cultivation

The

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 ...

'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 A hedge or hedgerow is a line of closely spaced (3 feet or closer) 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 ...

due to its density and strong curved thorns. Such hedges have been grown for over 50 years at

Oklahoma State University Oklahoma State University (informally Oklahoma State or OSU) is a public land-grant research university in Stillwater, Oklahoma, United States. The university was established in 1890 under the legislation of the Morrill Act. Originally known ...

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 the City of London and several boroughs. Over time, a number of definitions have been used to define the scope of Central London for statistics, urban planning and local gove ...

, mature specimens of the trifoliate orange can be seen in the gardens of

St Paul's Cathedral St Paul's Cathedral, formally the Cathedral Church of St Paul the Apostle, is an Anglican cathedral in London, England, the seat of the Bishop of London. The cathedral serves as the mother church of the Diocese of London in the Church of Engl ...

. 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). 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 ''Citrus'' is a genus of flowering trees and shrubs in the family Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, mandarins, lemons, grapefruits, pomelos, and limes. ''Citrus'' is native to S ...

(CTV).

As food

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 Marmalade (from the Portuguese ''marmelada'') is a fruit preserves, 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. It also has been made from lemons ...

. When dried and powdered, they can be used as a

condiment A condiment is a preparation that is added to food, typically after cooking, to enhance the Flavoring, flavour, to complement the dish or to impart a specific flavor. Such specific flavors generally add sweetness or pungency, or sharp or piquant ...

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 considered a member of the

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 ...

''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 Professor David John Mabberley , (born May 1948) is a British botanist, educator and writer. Among his varied scientific interests is the taxonomy of tropical plants, especially trees of the families Labiatae, Meliaceae and Rutaceae (in parti ...

and Dianxiang Zhang reunited all of Swingle's novel genera back into ''Citrus'' in 2008. Early phylogenetic analysis of trifoliate orange

plastid A plastid is a membrane-bound organelle found in the Cell (biology), cells of plants, algae, and some other eukaryotic organisms. Plastids are considered to be intracellular endosymbiotic cyanobacteria. Examples of plastids include chloroplasts ...

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 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 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) 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. Mos ...

, 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, 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 flesh of the fruit is segmented and varies in color from pale yellow to dark red. Grapefru ...

. 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