They are slow-growing evergreen shrubs or short trees, from 2.5 to 4.5 metres (8 to 15 ft) tall, with sparse branches, sometimes bearing small thorns. The leaves are dark glossy green, and the flowers pure yellow, similar to other citrus flowers, borne singly or clustered in the leaf-axils. The kumquat tree produces 30 to 50 fruit each year. The tree can be hydrophytic, and fruit is often found floating near the shore during the kumquat season.[citation needed]
Kumquats originated in China, appearing in literature dating to the 12th century. They have long been cultivated in Japan, and 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 Citrus.
Wikipedia: Cumquats






