Kumquats ( KUM-kwot), sometimes spelled cumquat, are a group of small, angiosperm, fruit-bearing trees in the family Rutaceae. The edible fruit closely resembles the orange (Citrus x sinensis) in color, texture, and anatomy, but is much smaller, being approximately the size of a large olive. They are native to southern China but have been cultivated for centuries in Japan and Southeast Asia. The kumquat is a fairly cold-hardy citrus. The taxonomy of kumquats is disputed. They were once classified as forming the historical genus Fortunella or placed within Citrus, sensu lato. Different classifications have assigned them ranging from a single species, Citrus japonica, to numerous species representing each cultivar. Recent genomic analysis defines three pure species, Citrus hindsii, C. margarita and C. crassifolia, with C. × japonica being a hybrid of the last two.
Etymology The English word kumquat is a borrowing of the Cantonese gām gwāt (IPA: [kɐ́m kʷɐ́t̚]; Chinese: 金橘), from gām 'golden' + gwāt 'orange'.
Description Kumquat plants have thornless branches and extremely glossy leaves. They bear dainty white flowers that occur in clusters or individually inside the leaf axils. The plants can reach a height from 2.5 to 4.5 meters (8 to 15 feet), with dense branches, sometimes bearing small thorns. They bear yellowish-orange fruits that are oval or round in shape. The fruits can be 2.5–5 centimeters (1–2 inches) in diameter and have a sweet, pulpy skin and slightly acidic inner pulp. The fruit is often eaten whole by humans and has a taste that is sweet and somewhat sour. Kumquat trees are self-pollinating.
Species Citrus taxonomy is complicated and controversial. Different systems place various types of kumquats in different species or unite them into as few as two species. Botanically, many varieties of kumquats are classified as their own species, rather than cultivars. 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 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, 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. 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. A 2020 review concluded that genomic data were insufficient to reach a definitive conclusion on which kumquat cultivars represented distinct species. In 2022, a genome-level analysis of cultivated and wild varieties drew several conclusions. The authors found support for the division of kumquats into subgenera: Protocitrus, for the wild Hong Kong variety, and Eufortunella for the cultivated varieties, with a divergence predating the end of the Quaternary glaciation, perhaps between two ancestral populations isolated south and north, respectively, of the Nanling mountain range. Within the latter group, the oval, round, and Meiwa kumquat each showed a level of divergence greater than between other recognized citrus species, such as between pomelo and citron, and hence each merits species-level classification. Though Swingle had speculated that the Meiwa kumquat was a hybrid of oval and round kumquats, the genomic analysis suggested instead that the round kumquat was an oval/Meiwa hybrid.
Hybrids
Hybrid forms of the kumquat include the following:
Calamansi: mandarin orange x kumquat Citrangequat: citrange x kumquat Limequat: key lime x kumquat Mandarinquat: Satsuma mandarin x kumquat Procimequat: limequat x kumquat Sunquat: Meyer lemon (?) x kumquat Yuzuquat: yuzu x kumquat
Origin and distribution The kumquat plant is native to Southern China. The first historical reference to kumquats appears in literature of China from at least the 12th century. They have been cultivated for centuries in other parts of East Asia, South Asia, and Southeast Asia. They were introduced into Europe in 1846 by Robert Fortune, collector for the London Horticultural Society, and have spread across the world.
Cultivation
Kumquats are much hardier than citrus plants such as oranges. Sowing seeds in the spring is ideal because the temperature is pleasant, with more chances of rain and sunshine. This also gives the tree enough time to become well established before winter. Early spring is the best time to transplant a sapling. They do best in direct sunlight (needing 6–7 hours a day) and are planted directly in the ground. Kumquats do well in USDA hardy zones 9 and 10 and can survive in temperatures as low as 18 degrees Fahrenheit (−8 degrees Celsius). On trees mature enough, kumquats will form in about 90 days. In cultivation in the UK, Citrus japonica has gained the Royal Horticultural Society's Award of Garden Merit (confirmed 2017).
Propagation Kumquats do not grow well from seeds and so are vegetatively propagated by using rootstock of another citrus fruit, air layering, or cuttings.
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