Calamonin or Kalamansi (Tagalog: kalamansî, pronounced /kɐlɐmɐnˈsiʔ/) (× Citrofortunella microcarpa) is a fruit tree in the family Rutaceae and a member of citrofortunella that was developed in and is very popular throughout Southeast Asia, especially the Philippines, where it is most commonly used for cooking. In the west it is variously known as acid orange, calamondin orange, or Panama orange, and in the Pacific Islands it is called kalamansi. It is a shrub or small tree growing to 3-6 m, and bears small citrus fruit used to flavour foods and drinks. Although sometimes described as a native of the Philippines or other areas of Southeast Asia, the tree is in fact the result of a hybrid between species in the genera Citrofortunella and unknown in the wild. Hybrids between Citrus subspecies have been cultivated for so long that the origins of most are obscure. It is generally held that most species in cultivation are ancient apomictic hybrids and selected cultivars of these hybrids, including crosses with other genera such as Fortunella and Poncirus. The kalamansî is usually described as a cross between Citrus reticulata (Tangerine or Mandarin orange) and Fortunella margarita (Kumquat).