Citrus aurantium, the sour orange (also known as bitter or Seville orange) is a thorny tree up to 10 m tall in the Rutaceae (citrus family) that originated in southeastern China and Myanmar, and is now commercially cultivated primarily in Spain, southern France, China, and Japan for its use in marmalade and candied peels and as an ornamental. The closely related bergamot, which is variously classified as a subspecies (C. aurantium subsp. bergamia) or a separate species (C. bergamia), is thornless and not as tall (to 5 m). Citrus species hybridize readily, and classifications of them vary considerably; in some classifications, this species is considered C. X aurantium, a hybrid between C. maxima and C. reticulata. The original species is now considered critically endangered in its native range, where it is found only in isolated populations in the regions of Hsinchu and Taitung, in China.
The sour orange tree has alternate, evergreen, minutely toothed oval to oblong leaves up to 13.75 cm (5 in) long, with broadly winged petioles (leaf stems). Leaves are aromatic and covered with small oil glands. Flowers, which are about 3.75 cm wide (1.5 in) are fragrant, with 5 slender white petals and 24 yellow stamens, and may occur singly or in small clusters. The fruit is round to somewhat flattened, up to 8 cm (3.12 in) wide, and ripens to orange or reddish orange. The fruit rind or peel is thick and aromatic, with a rough surface dimpled with tiny oil glands. The flesh or pulp is separated into 10 to 12 segments, with few to many hard seeds, and is often hollow in the middle. In addition to being cultivated for its fruit, sour orange is also used as a hardy rootstock for many other citrus varieties.
Sour oranges are sour from high acidity, as well as bitter, are not considered edible fresh; they are primarily processed into marmalade. The juice may be used as a flavoring or similar to vinegar in some regional cuisines. “Bitter orange oil,” extracted from the peels, is used to flavor candy, chewing gum, baked goods, soft drinks, and liqueurs, including Curaçao, Cointreau, and Grand Marnier, as well as in the bitter orange French “sauce bigarande” to accompany roast duck. The popular Italian beverage, chinotto, comes from the sour orange variety, Citrus uranium var. myrtifolia.
Bergamot, which is likely of hybrid origin, is prized primarily for its highly aromatic oil, which was an ingredient in eau de cologne, the perfume originally developed in Cologne, Germany during the 17th century. It is also used to flavor Earl Grey tea. Bergamot is produced mostly in the Calabrian region of Italy.
(Bailey et al. 1976, Morton 1987, van Wyk 2005, Wikipedia 2012.)
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