Zereshk (Barberries) is an ancient berry which grows in Europe and the Middle East. Iran is one of the few countries in the world where people still use Zereshk in their daily cooking.
You may find Zereshk and saffron being served on top of the steamed rice more like a decoration to it. In some place in Iran, people may layer the rice with Zereshk and steam them together. The sour flavor of the Zereshk creates a good combination with chicken.