I've added sumac to a few citrus dishes like this cake I baked on the last full moon of winter. It pairs well with lemon, orange and berries, adding a unique tart punch and an interesting element to citrus.
Sumac is native to the Middle East, and Western Asia. It's a small flowering tree in the cashew family and the berries are used. Before the Greeks encountered lemon it was widely used to add a sour element to dishes, and is frequently dried and sprinkled over food the way paprika would be. It is believed to have antimicrobial and antioxidant properties and has been used as a dying agent for wool and tanning leather since ancient times. The word sumac means "red" in Syriac, Arabic, Medieval Latin and Old French.