The kumquats or cumquats are a group of small fruit-bearing trees in the genus Fortunella related to the 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 the orange (Citrus sinensis) but is smaller and is often oval.
They are slow-growing, evergreen shrubs or small trees, from tall, with dense branches, sometimes bearing small thorns. The leaves are dark glossy green, and the flowers pure white, similar to other citrus flowers, borne singly or clustered in the leaf-axils. The kumquat tree produces 80 to 100 fruit each year. The tree can be hydrophytic, and fruit is often found floating near the shore during the kumquat season.
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:
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, long and wide. Depending on variety, peel colour ranges from yellow to red. A Nagami kumquat has an oval shape, while a Marumi kumquat is round.
They are much hardier than other citrus plants such as oranges. The 'Nagami' kumquat requires a hot summer, ranging from 25 to 38°C (77 to 100°F), but can withstand frost down to about without injury. It grows in the tea balls 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.
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 can also be sliced and added to salads. A liqueur can also be made by macerating kumquats in vodka or other clear spirit.
The Cantonese often preserve kumquats in salt or sugar. 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 dehydration into the salt. The fruit in the jar becomes 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 and still keep taste.
In Taiwan, kumquats are a popular addition to both hot and iced tea.
Variants of the kumquat are grown specially in India.
Names in other Asian languages include: