A fruit tree in the family Rutaceae 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. In the Philippines it is called calamansi or lemoncito. 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 genus Citrus and unknown in the wild.