Bitter Orange, also known as Seville Orange or Sour Orange, is the fruit of the citrus tree Citrus x aurantium – an evergreen tree with long spines and aromatic flowers. Native to Southeast Asia, it is thought that Bitter Orange is likely a cross between the pomelo and the mandarin orange. The membranes and pulp of the fruit are very sour, bitter and inedible, but the peel of Bitter Orange is used to flavor a variety of foods and beverages, including marinades, marmalade and liqueurs.