Orange and other citrus trees are an iconic part of the Southern California landscape. They are ideally suited to growing in only a few mild-winter areas of the United States including Central to Southern California, Southern Florida, and Southern Texas. They can be grown in other areas, but usually with special care, with only limited species and varieties, or in containers for indoor growing during cold winters. Oranges and other citrus are so common in parts of Southern California that they sometimes go unappreciated or even ignored. As Aesop said, familiarity breeds contempt; orange and other citrus being taken for granted in their California growing range is in contrast to gardeners in colder regions who sometimes go to great lengths to keep a small number of citrus trees alive, achieve fruit set under adverse conditions, and hopefully, once in a while, harvest a few homegrown, tree-ripened fruits.
Oranges are small trees in the Citrus genus and the family Rutaceae, the rue family, with many of its numerous plant members known for producing strongly aromatic, flavorful, or medicinal leaves and/or fruit. Oranges commonly grown in the home garden and landscape include sweet, mandarin, blood, and sour or bitter oranges. Sweet oranges, and sweet citrus in general, require heat to develop high sugar content in fruits; while sour oranges, and sour citrus in general, are often able to produce good-quality fruit in cooler climates.
The agricultural origins and exact native range of oranges remains unknown; it is believed that oranges were first cultivated around 2500 BC in China, and originated in Southern China, Northeast India, and/or parts of Southeast Asia. While various citrus were known in Italy as early as the 11th Century, sweet oranges were unknown in the West until the late 15th Century, after which they spread rapidly, and were known throughout Europe by the mid-17th Century.
Oranges were used for centuries as a means to prevent scurvy, a disease caused by vitamin C deficiency that killed millions of sailors throughout history. Areas along trade routes with suitable climates were commonly planted with orange trees. Spanish missionaries introduced the first citrus trees to California in the mid-18th century, and since then, orange trees have spread throughout Southern California, and become an important part of the California produce industry. Orange trees are now grown in Mediterranean, subtropical, semitropical, and tropical regions worldwide, and may be the most cultivated fruit tree in the world.
Oranges are known for their high vitamin C content, but also contain dietary fiber, thiamin, and potassium. One medium-sized orange can contain up to 100% or more of the USDA recommended daily vitamin C.