Citrus
Family Rutaceae
Citrus sp., citrus (Cit. sp 1), are small trees or shrubs, up to 10 m high, with glandular tissues in all parts, and simple leaves with a winged leaf-stalk and in many species with a spine in the leaf axil. The flowers (Cit. sp 2) are singly or in small axillary clusters, usually white and sweet scented, 2.5-4 cm across, with numerous stamens and a superior ovary (Cit. sp 3). The fruit is a berry known as a hesperidium, with a leathery yellow or orange peel, consisting of thin-walled parenchyma, the exocarp, which is rich in oil glands. During the ripening of the fruit, the chlorophyll of the green fruit is replaced by xanthophyl and carotene, changing the colour of the fruit from green to yellow and orange. The inner colourless section of the peel, the mesocarp, is composed of elongated cells with large intercellular spaces. The inner layer of the fruit wall, the endocarp, consists of a thin membrane surrounding the carpels or segments. From the inner carpel walls multicellular hairs grow out and fill with juice as the fruit develops, providing the edible portion of the fruit. The juice contains sugars and acids, and during ripening the amount of acid decreases and that of sugars increases. In between the pulp vesicles the seeds are situated.
Distribution
All cultivated species of Citrus are believed to be of Southeast Asian origin. When man started cultivating types with edible juice, the resulting hybridisation produced a large group of varieties. Today Citrus species are grown throughout the tropics and subtropics between 45 degrees North and 35 degrees South. Most of the commercial production (Cit. sp 4) is in subtropical regions.
Use
Fruits with sweet juice are eaten fresh. Also large amounts are squeezed, the juicebeing used in a variety of drinks. The peel, as well as the flowers and leaves, are a source of essential oils, used in flavouring and perfumery, and of pectin. Some species provide citric acid and candied peel. See the different species.