Calamondin

A naturally occurring hybrid between a mandarin and a kumquat, calamondin has been cultivated in the Philippines for centuries, where it remains a genuine kitchen staple — known there as calamansi, its intensely sour juice is the base for the traditional dipping sauce used with grilled and fried foods across Filipino cuisine, and it is also a common substitute for lime or lemon in everyday cooking. It spread to the West largely as an ornamental container plant, valued as much for its near-constant flowering and fruiting as for the fruit itself, though it retains a devoted following among cooks specifically drawn to that intense, distinctive sourness.