The Flat lemon (Citrus depressa) belongs to Rutaceae (the Citrus family). It is an evergreen shrub that is distributed in the Nansei Islands in Japan, Amami Oshima and Okinawa, as well as Taiwan. The leaves are elliptic, the branches have thorns, and the height is about 3-5 m. White flowers bloom in spring, and the fruits ripen yellow-orange from November to December. The Japanese name comes from the Okinawan dialects "sii (sour)" and "kasha (feed)". It is also known as "Hirami lemon". Since fruits have a strong acidity, they are used as a raw material for juice and also for medicinal purposes.