Three types of fruit are grouped within the sour oranges:
Rootstock - this is the most common type of sour orange and is used as an ‘underground’ (root) foundation for other citrus to be budded to and grown, primarily ‘sweet oranges’. The most well-known of this type is the Seville orange which as noted in the UC Riverside collection, “Seville sour orange is the variety of sour orange traditionally used to make orange marmalade. The tree is attractive, large, vigorous, and cold tolerant. The fruit is medium-large, round, with a depressed apex, and has pebbled dark orange rind. Seville fruits mature in winter and are seedy, bitter, and acidic. Commercially, the fruits are valued for their oil content and juice. The fragrant flowers are used in China to flavor tea, and in Europe the flowers are the source of oil of neroli, used in perfume manufacture.”
Bittersweet - the fruit of the bittersweet orange is similar to the common type but less acidic. The description from The Citrus Industry Vol 1 (1967) reads, “Formerly thought to be a hybrid of the sweet and sour oranges, the weight of evidence suggests that the bittersweet orange originated as a mutation from the latter. It appears to be… described… as the sweet-fruited bitter orange of the Mediterranean basin. It seems likely that the Spanish took this orange to both Florida and South America, for it was early found in the former and occurs extensively in Paraguay where it comprises an important source of oil of petit grain.”
Ornamental - the fruit of this type of sour orange variant are grown primarily for the flower and oils. Probably best known is the Bergamot, again, as described in The Citrus Industry Vol 1 (1967), “While the distinctive fruit of the bergamot (bergamotto of Italy, bergamote of France) is sometimes referred to as an orange, its resemblances to the oranges are so remote or lacking that it seems best to employ the European usage. Both the origin of the name and its significance are obscure… A distinctive characteristic of both foliage and fruits is the strongly pungent and agreeably aromatic oil… The bergamot has been known in the Mediterranean for several centuries, the distinctive and desirable characteristics of its oil having been recognized as early as 1750.
For reasons that are not clear, the commercial culture of this fruit, which is grown primarily for the rind oil, is virtually confined to the province of Calabria in southern Italy, where the most recent statistics indicate a total planting of approximately 7,500 acres. While the tree grows and bears well in Sicily and in portions of North Africa and elsewhere, reportedly the oil is highly variable, inferior in quality, and therefore unprofitable.
Bergamot oil is commercially important because it constitutes the base of cologne water (eau de cologne), perhaps the most widely used toilet water, and also has other perfumery uses… An important byproduct of the highly acid juice in the oil extraction process is citrate of lime or citric acid."
The Sour Oranges
Special thanks to Univercity of California, Riverside | College of Natural and Agricultural Sciences
for use of the many carefully photographed species of citrus from their archives.