Citrus aurantium

The bitter orange, sour orange, Seville orange, bigarade orange, or marmalade orange is the hybrid citrus tree species Citrus × aurantium, and its fruit. It is native to Southeast Asia and has been spread by humans to many parts of the world. It is a cross between the pomelo, Citrus maxima, and the wild type mandarin orange, Citrus reticulata. The bitter orange is used to make essential oil, used in foods, drinks, and pharmaceuticals. The Seville orange is prized for making British orange marmalade.