Sudachi (Citrus sudachi) is a small, round, green Japanese citrus picked while still unripe and prized almost entirely for its sharp, fragrant juice and aromatic zest rather than its sparse flesh. A speciality of Tokushima Prefecture on Shikoku, it is squeezed over grilled fish, soba and somen noodles, matsutake mushrooms and sashimi, and stirred into ponzu, dressings and drinks, where it brings a cleaner, more herbal tartness than lemon — green, almost piney, with a cooling floral lift.