Citrus fruits are the fruits of trees or shrubs from the plant genus Citrus. The Citrus genus has been in cultivation for thousands of years. Its cultivation is already mentioned in Chinese chronicles dating back to 2200 BCE. As a result of this centuries-long cultivation, thousands of cultivars exist today.
The fruit consists of several layers. Citrus fruits can be eaten directly, but are also used as a flavoring agent. Furthermore, they are often pressed into juice.
Many hybrids and cultivars exist. Most citrus fruits are very juicy and contain a lot of vitamin C. The trees only grow in warm countries, such as Spain, Greece, Italy, and Israel.
The cradle of all citrus fruit lies in Southeast Asia, and archaeological evidence for citrus cultivation dates back to 2100 BCE. The knobby citron is the least known of the three ancestral citruses, yet it was the first citrus fruit to reach the Middle East and the Mediterranean. The orange was introduced to Europe by the Portuguese in the 16th century. The mandarin arrived in 1805.
Contrary to what was previously claimed, there are only three ‘true’ citrus species: the pomelo or Citrus grandis, the mandarin or Citrus reticulata, and the citron, Citrus medica. The orange, for example, is not actually a separate species, but a hybrid. The status of genera such as Fortunella (referring to kumquat) and Poncirus is disputed. According to the Flora of China, it is not useful to consider these as separate genera, and Fortunella and Poncirus are synonyms of Citrus.