Citrus japonica

Classification System: APG IV

Superregnum: Eukaryota
Regnum: Plantae
Cladus: Angiosperms
Cladus: Eudicots
Cladus: Core eudicots
Cladus: Rosids
Cladus: Eurosids II
Ordo: Sapindales

Familia: Rutaceae
Subfamilia: Aurantioideae
Tribus: Aurantieae
Subtribus: Citrinae
Genus: Citrus
Species: Citrus japonica
Name

Citrus japonica Thunb. (1780)
Synonyms

Atalantia hindsii (Champ. ex Benth.) Oliv.
Citrus hindsii (Champ. ex Benth.) Govaerts
Citrus inermis Roxb.
Citrus japonica subf. crassifolia (Swingle) M.Hiroe
Citrus japonica subf. hindsii (Chapm. ex Benth.) M.Hiroe
Citrus madurensis Lour.
Citrus margarita Lour.
Citrus × nobilis subf. kinokumi (Tanaka) M.Hiroe
Citrus × nobilis var. microcarpa Hassk.
Fortunella bawangica C.C.Huang
Fortunella crassifolia Swingle
Fortunella hindsii (Champ. ex Benth.) Swingle
Fortunella japonica (Thunb.) Swingle
Fortunella margarita (Lour.) Swingle
Fortunella venosa (Champ. ex Benth.) C.C.Huang
Sclerostylis hindsii Champ. ex Benth.
Sclerostylis venosa Champ. ex Benth.

Distribution
Native distribution areas:

Continental: Asia-Temperate
Regional: China
China Southeast, Hainan
Introduced into:
Assam, Cuba, Dominican Republic, Gambia, Haiti, Japan, Korea, Puerto Rico, Trinidad-Tobago, Vietnam

References: Brummitt, R.K. 2001. TDWG – World Geographical Scheme for Recording Plant Distributions, 2nd Edition
References
Primary references

Thunberg, C.P. 1780: Nova Acta Regiae Societatis Scientiarum Upsaliensis 3: 208

Links

Govaerts, R. et al. 2021. Citrus japonica in Kew Science Plants of the World online. The Board of Trustees of the Royal Botanic Gardens, Kew. Published on the internet. Accessed: 2021 Feb 06. Reference page.
International Plant Names Index. 2021. Citrus japonica. Published online. Accessed: Feb 06 2021.
Tropicos.org 2021. Citrus japonica. Missouri Botanical Garden. Published on the internet. Accessed: 2021 Feb 06.
Hassler, M. 2021. Citrus japonica. World Plants: Synonymic Checklists of the Vascular Plants of the World In: Roskovh, Y., Abucay, L., Orrell, T., Nicolson, D., Bailly, N., Kirk, P., Bourgoin, T., DeWalt, R.E., Decock, W., De Wever, A., Nieukerken, E. van, Zarucchi, J. & Penev, L., eds. 2021. Species 2000 & ITIS Catalogue of Life. Published on the internet. Accessed: 2021 Feb 06. Reference page.

Vernacular names
English: Kumquat
日本語: キンカン
lea faka-Tonga: kamikuati

Kumquats (/ˈkʌmkwɒt/;[2] Chinese: 金桔, gāmgāt or jīnjú), or cumquats in Australian English, are a group of small fruit-bearing trees in the flowering plant family Rutaceae. They were previously classified as forming the now-historical genus Fortunella, or placed within Citrus, sensu lato.

The edible fruit closely resembles the orange (Citrus sinensis) in color and shape but is much smaller, being approximately the size of a large olive. Kumquat is a fairly cold-hardy citrus.

Etymology

The English name "kumquat" derives from the Cantonese kamkwat (Chinese: 金橘; pinyin: jīnjú; Jyutping: gām gwāt; lit. 'golden mandarin orange').[3]
Illustration by Walter Hood Fitch
Origin

The kumquat plant is native to China.[4][5] The earliest historical reference to kumquats appears in Imperial literature from the 12th century. They have long been cultivated in other parts of East Asia (Japan and Taiwan), South Asia (India), and Southeast Asia (especially the Philippines). They were introduced to Europe in 1846 by Robert Fortune, collector for the London Horticultural Society, and shortly thereafter were taken to North America.[6]
Description

They are slow-growing evergreen shrubs or short trees that stand 2.5 to 4.5 meters (8 to 15 ft) tall, with dense branches, sometimes bearing small thorns. The leaves are dark glossy green, and the flowers are white, similar to other citrus flowers, and can be borne singly or clustered within the leaves' axils. Depending on size, the kumquat tree can produce hundreds or even thousands of fruits each year.[4]
Varieties

Citrus taxonomy is complicated and controversial. Different systems place different types of kumquat in different species, or unite them into as few as two species. Historically they were viewed as falling within the genus Citrus, but the Swingle system of citrus taxonomy elevated them to their own genus, Fortunella. Recent phylogenetic analysis suggests they do indeed fall within Citrus. Swingle divided the kumquats into two subgenera, the Protocitrus, containing the primitive Hong Kong kumquat, and Eufortunella, comprising the round, oval kumquat, Meiwa kumquats,[7] to which Tanaka added two others, the Malayan kumquat and the Jiangsu kumquat. Chromosomal analysis suggested that Swingle's Eufortunella represent a single 'true' species, while Tanaka's additional species were revealed to be likely hybrids of Fortunella with other Citrus, so-called xCitrofortunella.[8] One recent genomic analysis concluded there was only one true species of kumquat, but the analysis did not include the Hong Kong variety seen as a distinct species in all earlier analyses.[9] A recent review concluded that genomic data were insufficient to reach a definitive conclusion on which kumquat cultivars represented distinct species.[10]
Round kumquat

The round kumquat, Marumi kumquat or Morgani kumquat (retaining the name Citrus japonica or Fortunella japonica when kumquats are divided into multiple species), is an evergreen tree that produces edible golden-yellow fruit.[4] The fruit is small and usually spherical but can be oval shaped. The peel has a sweet flavor, but the fruit has a distinctly sour center. The fruit can be eaten cooked but is mainly used to make marmalades, jellies, and other spreads. It is grown in Luxembourg and can be used in bonsai cultivation. The plant symbolizes good luck in China and other Asian countries, where it is often kept as a houseplant and given as a gift during the Lunar New Year. Round kumquats are more commonly cultivated than other species due to their high cold tolerance.[4]
Oval kumquat

The oval kumquat or Nagami kumquat (Citrus margarita or Fortunella margarita if dividing Eufortunella kumquats into separate species) is ovoid in shape and typically eaten whole, skin and all.[4] The inside is still quite sour, but the skin has a very sweet flavour, so when eaten together an unusual tart-sweet, refreshing flavour is produced. The fruit ripens mid- to late winter and always crops very heavily, creating a spectacular display against the dark green foliage. The tree tends to be much smaller and dwarf in nature, making it ideal for pots and occasionally bonsai cultivation.[11]
'Centennial Variegated' kumquat
Kumquat
Kumquat (Chinese characters).svg
"Kumquat" in Chinese characters
Chinese name
Chinese 金橘
Literal meaning "golden orange"
Transcriptions
Vietnamese name
Vietnamese kim quất
Thai name
Thai ส้มจี๊ด
RTGS somchíd
Korean name
Hangul 금귤
Hanja 金橘
Transcriptions
Japanese name
Kanji 金柑
Transcriptions
Nepali name
Nepali muntala

The 'Centennial Variegated' kumquat cultivar arose spontaneously from the oval kumquat. It produces a greater proportion of fruit to peel than the oval kumquat, and the fruit are rounder and sometimes necked. Fruit are distinguishable by their variegation in color, exhibiting bright green and yellow stripes,[4] and by its lack of thorns.
Meiwa kumquat

The Meiwa kumquat (Citrus crassifolia or Fortunella crassifolia) was brought to Japan from China at the end of the 19th century, it has seedy oval fruits and thick leaves, and was characterized as a different species by Swingle.[7] Its fruit is typically eaten skin and all.
Hong Kong kumquat
Kumquats, raw

Nutritional value per 100 g (3.5 oz)
Energy	296 kJ (71 kcal)

Carbohydrates	15.9 g
Sugars	9.36 g
Dietary fiber	6.5 g

Fat	0.86 g

Protein	1.88 g

Vitamins	Quantity %DV^†
Vitamin A equiv. lutein zeaxanthin	2% 15 μg 129 μg
Thiamine (B1)	3% 0.037 mg
Riboflavin (B2)	8% 0.09 mg
Niacin (B3)	3% 0.429 mg
Pantothenic acid (B5)	4% 0.208 mg
Vitamin B6	3% 0.036 mg
Folate (B9)	4% 17 μg
Choline	2% 8.4 mg
Vitamin C	53% 43.9 mg
Vitamin E	1% 0.15 mg

Minerals	Quantity %DV^†
Calcium	6% 62 mg
Iron	7% 0.86 mg
Magnesium	6% 20 mg
Manganese	6% 0.135 mg
Phosphorus	3% 19 mg
Potassium	4% 186 mg
Sodium	1% 10 mg
Zinc	2% 0.17 mg
Link to USDA Database entry
Units μg = micrograms • mg = milligrams IU = International units
^†Percentages are roughly approximated using US recommendations for adults. Source: USDA FoodData Central

Hong Kong kumquat

The Hong Kong kumquat (Citrus hindsii or Fortunella hindsii) produces only pea-sized bitter and acidic fruit with very little pulp and large seeds. It is primarily grown as an ornamental plant, though it is also found in southern China growing in the wild.[12][13] Not only is it the most primitive of the kumquats, but with the kumquats being the most primitive citrus, Swingle described it as the closest to the ancestral species from which all citrus evolved.[7] While the wild Hong Kong kumquat is tetraploid, there is a commercial diploid variety, the Golden Bean kumquat with slightly larger fruit.[13]
Jiangsu kumquat

The Jiangsu kumquat or Fukushu kumquat (Citrus obovata or Fortunella obovata) bears edible fruit that can be eaten raw, as well as made into jelly and marmalade. The fruit can be round or bell-shaped and is bright orange when fully ripe. The plant can be distinguished from other kumquats by its distinctly round leaves. It is typically grown for its edible fruit and as an ornamental plant; it cannot withstand frost, however, unlike the round kumquat which has a high cold tolerance. These kumquats are often seen near the Yuvraj section of the Nayak Province. Chromosomal analysis showed this variety to be a likely hybrid.[8]
Malayan kumquat

The Malayan kumquat (Fortunella polyandra or Tanaka's Fortunella swinglei - in Citrus it would be C. x swinglei), from the Malay Peninsula where it is known as the "hedge lime" (limau pagar), is another hybrid, perhaps a limequat.[8][14] It has a thin peel on larger fruit compared to other kumquats.[14]
Cultivation and uses

Kumquats are much hardier than citrus plants such as oranges. The Nagami kumquat requires a hot summer, ranging from 25 °C to 38 °C (77 °F to 100 °F), but can withstand frost down to about −10 °C (14 °F) without injury.

The fruit is usually consumed whole with its peel and is sometimes used in fruit salads.[15]

In cultivation in the UK, Citrus japonica has gained the Royal Horticultural Society’s Award of Garden Merit[16] (confirmed 2017).[17]
Propagation and pollination

Kumquats do not grow well from seeds and so are vegetatively propagated by using rootstock of another citrus fruit,[4] air layering, or cuttings.[4]
Composition

The essential oil of the kumquat peel contains much of the aroma of the fruit, and is composed principally of limonene, which makes up around 93% of the total.[18] Besides limonene and alpha-pinene (0.34%), both of which are considered monoterpenes, the oil is unusually rich (0.38% total) in sesquiterpenes such as α-bergamotene (0.021%), caryophyllene (0.18%), α-humulene (0.07%) and α-muurolene (0.06%), and these contribute to the spicy and woody flavor of the fruit. Carbonyl compounds make up much of the remainder, and these are responsible for much of the distinctive flavor. These compounds include esters such as isopropyl propanoate (1.8%) and terpinyl acetate (1.26%); ketones such as carvone (0.175%); and a range of aldehydes such as citronellal (0.6%) and 2-methylundecanal. Other oxygenated compounds include nerol (0.22%) and Trans-lialool oxide (0.15%).[18]
Hybrids
Main article: Citrofortunella

Hybrid forms of the kumquat include the following:

Calamansi: mandarin orange x kumquat[19]
Citrangequat: citrange x kumquat
Limequat: key lime x kumquat
Orangequat: Satsuma mandarin x kumquat
Procimequat: limequat x kumquat
Sunquat: Meyer lemon (?) x kumquat
Yuzuquat: yuzu x kumquat

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