Citrus is a very popular port specialty, belonging to the subfamily Aurantioideae of the family Rutaceae. It is a tropical and subtropical evergreen fruit tree (except for the bitter orange). There are three genera used for economic cultivation: Poncirus, Citrus, and Fortunella. The beta-carotene (vitamin A precursor) content in citrus is second only to apricots and higher than other fruits. Citrus also contains various vitamins, as well as magnesium, sulfur, sodium, chlorine, and silicon. Citrus trees are long-lived, high-yielding, stable in production, and highly economically beneficial. They are the main fruit tree species in southern China and play a significant role in helping fruit farmers摆脱 poverty, and promoting rural economic development.