The Centennial Kumquat has a juicier flesh and a thinner peel than you're likely used to in the more ubiquitous Nagami variety. As with other 'quat varieties, you'll want to eat the whole fruit, as the peel is sweeter than the very tart flesh. It resulted from a spontaneous mutation in 1986, with one of its parent trees being a Nagami, and the other likely being a mandarin of some sort.