すだち,スダチSudachi

Sudachi (Citrus sudachi; Japanese: スダチ or 酢橘) is a small, round, green, Japanese citrus fruit that is a specialty of Tokushima Prefecture in Japan. It is a sour citrus, not eaten as fruit, but used as food flavoring in place of vinegar.

from Sudachi (Wikipedia) CC BY SA 3.0