Capers are grown in southern Italy, but particularly on the island of Pantelleria off the Sicilian coast. It's a perpetually windy island, where the olive trees are pruned to a squat form to survive heavy gusts, and the perfect place for caper plants, which grow close to the ground. The plant, capparis spinosa, belongs to the family capparidaceae. There are various varieties of caper, particularly in central Asia and India.
It is believed that capers originated in western or central Asia, though it has also been suggested that capparis spinosa is native to the Mediterranean Basin, which encompasses the Black Sea and other regions touching western Asia. The Roman author Pliny the Elder, who wrote about Sicilian cuisine, mentioned capers, and so did ancient Greeks. Capers similar to those of Pantelleria grow in many Mediterranean countries.
The caper itself is the bud of a flowering plant, and the stage at which the buds are harvested is very important. Some caper buds sold for the culinary market are quite large, reaching over two centimeters (almost an inch) in diameter, though most are much smaller.