Kumquats ( ), 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, . 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 (; ), from 'golden' + '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 , with dense branches, sometimes bearing small thorns. They bear yellowish-orange fruits that are oval or round in shape. The fruits can be 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.
{| class="wikitable"
|+Kumquat species
!Image
!Scientific name
!Common name
!Distribution
|-
|120px
|Citrus hindsii
|Hong Kong kumquat
|China
|-
|120px
|Citrus crassifolia
|Meiwa kumquat
|China, Japan
|-
|120px
|Citrus margarita
|oval kumquat, Nagami kumquat
|China, Japan
|-
|120px
|Citrus japonica
|round kumquat, Marumi kumquat, Morgani kumquat
|China, Japan
|-
|120px
|Citrus obovata
|Jiangsu kumquat, Fukushu kumquat
|China, Japan
|-
|120px
|Citrus swinglei
|Malayan kumquat
|Malay Peninsula
|}
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. and have spread across the world. (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.
The Centennial Variegated is another cultivar of the Nagami kumquat. It originated from the open pollination of a Nagami kumquat tree. The fruits are striped light green and yellow when underripe, and turn orange and lose their stripes when they ripen. They are oval-shaped, necked, 2.5 inches long, and have a smooth rind. They mature in winter. This cultivar arose spontaneously from the oval kumquat (Citrus margarita). It produces a greater proportion of fruit to peel than the oval kumquat, and the fruit is rounder and sometimes necked. Fruits are distinguishable by their variegation in color, exhibiting bright green and yellow stripes,
Uses
Nutrition
A raw kumquat is 81% water, 16% carbohydrates, 2% protein, and 1% fat (table). In a reference amount of , raw kumquat supplies of food energy and is a rich source of vitamin C (49% of the Daily Value), with no other micronutrients in significant content (table).
Essential oil
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. 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-linalool oxide (0.15%).