The kumquat flips citrus logic: sweet skin, sour inside
A kumquat looks like an orange shrunk to olive size, and you eat it whole. The surprise is that the peel is the sweet part while the pulp inside is tart. Its name is Cantonese for golden mandarin, and botanists still argue over how many species of this tiny fruit actually exist.
Kumquats are small citrus trees native to southern China and grown for centuries across Japan and Southeast Asia. Chinese writers mention them from at least the 12th century. Robert Fortune, collecting for the London Horticultural Society, brought them to Europe in 1846, and the old genus name Fortunella honours him. The trees reach roughly 2.5 to 4.5 metres, with glossy leaves, small white flowers and fruits 2.5 to 5 centimetres across. They pollinate themselves.
Classification has see-sawed. Walter Swingle's system lifted kumquats out of Citrus into their own genus, but newer phylogenetic work places them back inside it. Estimates have ranged from one species to one per cultivar, and a 2020 review said the genome data were not yet decisive. A 2022 genome-wide study supported splitting the wild Hong Kong kumquat from cultivated types, perhaps because ancestral populations were isolated on opposite sides of the Nanling mountains before the last glaciation ended. It judged the oval, round and Meiwa kumquats distinct enough to be separate species, and overturned Swingle's guess about hybrids: the round kumquat, not the Meiwa, looks like the cross.
Kumquats are unusually hardy for citrus, surviving down to about minus 8 degrees Celsius, and they like six or seven hours of direct sun. Because seeds do poorly, growers propagate them by grafting onto other citrus rootstock, air layering or cuttings. On mature trees fruit forms in about 90 days. In Britain the RHS has granted Citrus japonica its garden merit award.
Cultivars add variety. Centennial Variegated fruit is striped green and yellow until it ripens and loses the stripes, while Japan's Puchimaru is nearly seedless and resists citrus canker. The aroma comes mostly from limonene, about 93 per cent of the peel oil, with a small but unusual dose of spicy, woody compounds. A 100 gram serving provides 71 kilocalories and about half the daily value of vitamin C.
Source: Kumquat
