The kumquat is not of the genus citrus but is a close relative. It belongs to the genus fortunella. I have a plateful of the oval variety in front of me; they look like miniature orange footballs.
The kumquat shares many characteristics with citrus fruits : a color in the orange/yellow range, a thick skin, sectioned pulp, and an incredible juiciness. In one way it is different : the skin is sweet and the pulp is tart. Long admired in the Orient, it is gaining popularity in the United States.
Florida, being a citrus-producing state, has adopted it. In fact, it is often called "Florida's tiniest citrus product." St. Joseph, in Pasco County just 30 minutes north of Tampa, is the kumquat capital of the world. The kumquat is honored there every January with a Kumquat Festival featuring a cooking contest.
A very comprehensive node on the kumquat by meluseena
cites various culinary uses of the kumquat such as inclusion in salads and desserts, or in making jams, candied fruits and other sweets. The folks in Pasco County go a bit further than that. In past years enterprising recipe contestants have created kumquat and rum ice cream, kumquat salsa, kumquat pound cake, and kumquat chips.
I think it might be nice used in a salad I first met in Sydney, Australia. The original recipe was made with oranges but it should be possible to substitute kumquats.
Message me if you try this and like it; I just might go down to St. Joseph this coming weekend and sumbit the E2 Kumquat Special.
NSW Kumquat and Onion Salad
Take a quantity of washed and chilled kumquats. Do not remove the peel. Slice them thinly with a very sharp knife and put them in a bowl together with the juice. Peel and thinly slice a sweet red onion and mix together with the kumquat slices. Keep the proportions roughly one part onion to two parts kumquat. Sprinkle very sparingly with both salt and sugar and serve.
Keeping this (covered) in the fridge for a few hours before serving will intensify the flavor. If you want to get fancy, you can sprinkle some finely-chopped fresh mint on top just before serving.