Kumquats (/ˈkʌmkwɒt/ KUM-kwot),[1] or cumquats in Australian English, are a group of small, angiosperm, fruit-bearing trees in the family Rutaceae.

Recent genomic analysis defines three pure species, Citrus hindsii, C. margarita and C. crassifolia, with C. × japonica being a hybrid of the last two.

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.

[7] A 2020 review concluded that genomic data were insufficient to reach a definitive conclusion on which kumquat cultivars represented distinct species.

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.

In cultivation in the UK, Citrus japonica has gained the Royal Horticultural Society's Award of Garden Merit[14] (confirmed 2017).

[15] Kumquats do not grow well from seeds and so are vegetatively propagated by using rootstock of another citrus fruit,[11] air layering, or cuttings.

Fruit are distinguishable by their variegation in color, exhibiting bright green and yellow stripes,[11] and by its lack of thorns.

In a reference amount of 100 grams (3+1⁄2 ounces), raw kumquat supplies 296 kilojoules (71 kilocalories) of food energy and is a rich source of vitamin C (49% of the Daily Value), with no other micronutrients in significant content (table).

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.

[21] 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.

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.