Citrus depressa

Citrus depressa (Citrus × depressa, formerly C. pectinifera, Okinawan: シークヮーサー/シークァーサー, romanized: shiikwaasa, Japanese: ヒラミレモン, romanized: hirami remon or シークヮーサー, shiikwāsā, in English sometimes called shiikuwasha, shequasar, Taiwan tangerine, Okinawa lime, flat lemon, hirami lemon, or thin-skinned flat lemon, is a small citrus fruit often harvested and used when green, rich in flavonoids and native to East Asia (Taiwan and Okinawa Islands, Japan). Very sour, it is often used like lemon or lime to garnish dishes, but is also used to make jams, or a yellow juice, which can be thinned or sweetened. Its name is occasionally translated into English as calamansi (calamondin, Citrus × microcarpa), but this is a different fruit. Shiikwaasa is primarily produced in southwest Japan, in the northern region of the main Okinawa island, along with another indigenous Japanese citrus, the tachibana orange (Citrus tachibana). The two are not the only species of citrus currently growing on the island......read more on Wikipedia.