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Saffron is a spice derived from the flower of the saffron crocus (Crocus sativus), a species of crocus in the family Iridaceae. The flower has three stigmas, which are the distal ends of the plant's carpels. Together with its style, the stalk connecting the stigmas to the rest of the plant, these components are often dried and used in cooking as a seasoning and colouring agent. Saffron, which has for decades been the world's most expensive spice by weight, is native to Southwest Asia. Saffron is characterised by a bitter taste and an iodoform- or hay-like fragrance; these are caused by the chemicals picrocrocin and safranal. It also contains a carotenoid dye, crocin, that gives food a rich golden-yellow hue. These traits make saffron a much-sought ingredient in many foods worldwide. Saffron also has medicinal applications. The domesticated saffron crocus C. sativus is an autumn-flowering perennial plant unknown in the wild, and is a sterile triploid mutant of the eastern Mediterranean autumn-flowering Crocus cartwrightianus. According to botanical research, C. cartwrightianus originated in Crete, not—as was once generally believed—in Central Asia. The saffron crocus resulted when C. cartwrightianus was subjected to extensive artificial selection by growers who desired elongated stigmas. Being sterile, the saffron crocus's purple flowers fail to produce viable seeds—thus, reproduction is dependent on human assistance: the corms (underground bulb-like starch-storing organs) must be manually dug up, broken apart, and replanted. A corm survives for only one season, reproducing via division into up to ten "cormlets" that eventually give rise to new plants. The corms are small brown globules up to 4.5 centimetres (1.8 in) in diameter and are shrouded in a dense mat of parallel fibers.