Kumquats are a group of small fruit-bearing trees in the flowering plant family Rutaceae. They were previously classified as forming the now historical genus Fortunella, or placed within Citrus sensu lato. The edible fruit closely resembles the orange, but it is much smaller, being approximately the size and shape of a large olive. Kumquat is a fairly cold-hardy citrus.
Lemons are usually bigger, oval in shape and their rinds are thicker than that of a lime. Limes are usually smaller, more round in shape and the rind is thiner and smoother than that of the lemon. The green limes seen in the grocery store are only green because they were picked before they turned yellow.