Kumquat

Sometimes called Chinese oranges, these are the smallest, weirdest, and certainly the rarest of the common citrus fruits. In a contrary turnaround from others in this group, the tasty skin and zest are extraordinarily sweet and tasty, whilst the juicy insides are just the same as many oranges. The size of very small plums, they are often used as an expensive winter treat and can be eaten whole, just as they are, (yes really, I have tried them), or cooked with sugar, spices or spirits to make sweet compôtes and aromatic chutneys, and are often sliced whole and used in curries. The small fruiting trees are usually bred to be sterile, thus almost all commercial trees give fruits with no seeds. And so, although they grow true from seed, very few fruits actually contain good seeds, if any at all, hence the very high price.