Saffron is a spice derived from the flower of Crocus sativus, commonly known as the "saffron crocus". The vivid crimson stigma and styles, called threads, are collected and dried for use mainly as a seasoning and colouring agent in food. Saffron has long been the world's costliest spice by weight. Although some doubts remain on its origin, it is believed that saffron originated in Iran. However, Greece and Mesopotamia have also been suggested as the possible region of origin of this plant. Harold McGee states that it was domesticated in or near Greece during the Bronze Age. C. sativus is possibly a triploid form of Crocus cartwrightianus, which is also known as "wild saffron". Saffron crocus slowly propagated throughout much of Eurasia and was later brought to parts of North Africa, North America, and Oceania.