Sudachi

Sudachi (Citrus sudachi; Japanese: すだち or 酢橘) is a small, round, green citrus fruit of Japanese origin that is a speciality of Tokushima Prefecture in Japan. It is sour citrus, not eaten as fruit, but used as a food flavouring in place of lemon or lime. Genetic analysis shows it to be the product of a cross between yuzu and another citrus akin to the koji and Tachibana orange.

Cultivated for centuries in parts of Japan, and perhaps nearly as well known as another sour citrus, the yuzu in that country, it has been considered an "indispensable companion" to eating matsutake mushroom. The ponzu (ポン酢, "pon vinegar"), the squeezed citrus juice used as an alternative to vinegar uses sudachi among other bitter oranges (kabosu or yuzu juices, and daidai) as an ingredient.