The Kumquats or cumquats are a group of small fruit-bearing trees in the subgenus Fortunella of the genus Citrus in the flowering plant family Rutaceae, often segregated as a separate genus Fortunella. The edible fruit (which is also called kumquat) closely resembles that of other Citrus but is smaller.

They are slow-growing, evergreen shrubs or small trees, from 2.5-4.5 m tall, with dense branches, sometimes bearing small thorns. The leaves are dark glossy green, and the flowers pure white, similar to citrus flowers, borne singly or clustered in the leaf-axils.

Kumquats originated in China (they are noted in literature dating to the 12th century), and have long been cultivated there and in Japan. They were introduced to Europe in 1846 by Robert Fortune, collector for the London Horticultural Society, and shortly thereafter into North America. Originally placed in the genus Citrus, they were transferred to the genus Fortunella in 1915, though subsequent work (Burkill 1931, Mabberley 1998) favours their return to inclusion in Citrus.

Four or five species are currently accepted:

• Citrus crassifolia (syn. Fortunella crassifolia) - Meiwa Kumquat
• Citrus hindsii (syn. Fortunella hindsii) - Hong Kong Kumquat
• Citrus japonica (syn. Fortunella japonica, C. margarita, F. margarita) - Marumi or Nagami Kumquat
• Citrus obovata (syn. Fortunella obovata) - Jiangsu Kumquat
• Citrus polyandra (syn. Fortunella polyandra) - Malayan Kumquat

Kumquats readily hybridise with other members of the genus Citrus and with the closely related Poncirus. These hybrids are known as Citrofortunella; examples include the limequat, orangequat, and calamondin.

In appearance the kumquat fruit (generally called simply "kumquat") resembles a miniature oval orange, 3-5 cm long and 2-4 cm wide. Depending on variety, peel color ranges from yellow to red. A Nagami kumquat has an oval shape, while a Marumi kumquat is round.

Kumquat fruit is generally in season from late autumn to mid-winter, and can be found in most food markets with other produce.

Cultivation and uses
Kumquats are cultivated in China, Taiwan, Southeast Asia, Japan, Europe (notably Corfu, Greece), and the southern United States (notably Florida).

Climate
They are much hardier than citrus plants such as oranges. The 'Nagami' kumquat requires a hot summer, ranging from 25 ºC to 38º C, but can withstand frost down to about −10 °C without injury. It grows in the tea regions of China where the climate is too cold for other citrus fruits, even the Mikan (also known as the Satsuma) orange. The trees differ also from other Citrus species in that they enter into a period of winter dormancy so profound that they will remain through several weeks of subsequent warm weather without putting out new shoots or blossoms. Despite their ability to survive low temperatures, as in the vicinity of San Francisco, California, the kumquat trees grow better and produce larger and sweeter fruits in warmer regions.

Propagation
Kumquats are rarely grown from seed as they do not do well on their own roots. In China and Japan they are grafted onto the trifoliate orange (Poncirus trifoliata). This has been found the best rootstock for kumquats in northern Florida and California and for dwarfing for pot culture. Sour orange and grapefruit are suitable rootstocks for southern Florida. Rough lemon is unsatisfactory in moist soils and tends to be too vigorous for the slow-growing kumquats.

Uses

Kumquats are frequently eaten raw. As the rind is sweet and the juicy centre is sour, the raw fruit is usually consumed either whole, to savour the contrast, or only the rind is eaten. The fruit is considered ripe when it reaches a yellowish-orange stage, and has just shed the last tint of green. A variety of kumquat grown in Hong Kong has a rather sweet rind compared to the rinds of other citrus fruits.

Culinary uses include: candying and kumquat preserves, marmalade, and jelly.

Kumquats appear more commonly in the modern market as a martini garnish, replacing the classic olive. They add a nice zest to a salad; just slice and toss them in. A liqueur can also be made by macerating kumquats in vodka or other clear spirit.

The Cantonese often preserve kumquats in salt. A batch of the fruit is buried in dry salt inside a glass jar. Over time, all the juice from the fruit is extracted through osmosis into the salt. The fruits in the jar become shrunken, wrinkled, and dark brown in color, and the salt combines with the juice to become a dark brown brine. A few salted kumquats with a few teaspoons of the brine/juice may be mixed with hot water to make a remedy for sore throats. A jar of such preserved kumquats can last several years.

In Taiwan, kumquats are a popular addition to both hot and iced tea.

Etymology
The English name "kumquat" derives from the Cantonese pronunciation gam gwat (given in Jyutping romanization; literally "golden orange"). The alternate name, also pronounced gam1 gwat1 in Cantonese (gān jú in Mandarin, literally "large tangerine orange") is now more commonly written by Cantonese speakers.

Names in other Asian languages include:

• Japanese: kinkan
• Korean: geumgyul
• Mandarin: jīnjú
• Thai: somchíd
• Vietnamese: cam quất (derived from the Cantonese) or, less commonly, (quả) kim quất (if transliterated from the characters into Sino-Vietnamese; "quả" is the Sino-Vietnamese prefix for "fruit")