calamondin

:  a small hybrid citrus tree (Citrofortunella microcarpa synonym Citrofortunella mitis synonym Citrus mitis) of warm regions cultivated chiefly as an ornamental; also :  its small, tart, orange fruit resembling a mandarin or kumquat and yielding an acidic juice used especially as a flavoring agent or in beverages and marmalades ◆While the calamondin has been widely grown in the Philippines and Indonesia, it is thought to be native to China.