Citrus includes all species that originated from the citrus family, Oval Kumquat family, and hardy-orange trees.  In orchards, only the tangerine species in the citrus family is cultivated.  
Tangerine trees are green shrubs or small arbors with thorns on branches. Tangerine is alkali food that helps our metabolism and strengthens the skin and membranes.
We use tangerine inside out and even its dried peels are used as oriental medicine and bath aroma.
Popular species include citron, lemon, grape fruit, sour orange, sweet orange, mandarin orange, hardy-oranges, and Oval Kumquat.  Among these, mandarin orange has the highest resistance to low temperature and is most widely cultivated in Jeju.  It is cultivated for food and often used in processed foods, such as canned fruit and juice.