Kumquats, or cumquats in Australian English, are a group of small fruit-bearing trees in the flowering plant family Rutaceae. Their taxonomy is disputed. They were previously classified as forming the now-historical genus Fortunella or placed within Citrus, sensu lato. Different classifications have alternatively assigned them to anywhere from a single species, C. japonica, to numerous species representing each cultivar. Recent genomic analysis would define three pure species, Citrus hindsii, C. margarita and C. crassifolia, with C. x japonica being a hybrid of the last two.
The edible fruit closely resembles the orange (Citrus sinensis) in color and shape but is much smaller, being approximately the size of a large olive. The kumquat is a fairly cold-hardy citrus.