Citrus depressa

Citrus depressa (Citrus × depressa, formerly C. pectinifera, Okinawan シークヮーサー or シークァーサー shīkwāsā, Japanese ヒラミレモン hirami remon), in English sometimes called Taiwan tangerine, flat lemon, hirami lemon, or thin-skinned flat lemon, is a small, green citrus fruit rich in flavonoids and native to Taiwan and Okinawa, Japan. Very sour, it is often used like lemon or lime to garnish dishes, but is also used to make a yellow juice, which can be thinned or sweetened.

Its name is occasionally translated into English as kalamansî, but strictly speaking this is a different fruit.