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Following a long history of cultivation, coupled with the ease by which hybridisation can occur within the genus Cistus, it has become very difficult to devise a workable taxonomy for all the commercially significant taxa, Previous systems have recognised anything from 1 - 167 ‘good’ species in the genus. Work is ongoing to produce a workable monograph of the genus and in the meantime we are following the the treatment proposed by D.J. Mabberley (A classification for edible citrus: an update, with a note on Murraya (Rutaceae), in Telopea 25: 271-284, 2022).
The parentagege of Citrus × aurantium is (male) C. reticulata × (female) C. maxima, including many back-crosses. This taxa can be subdivided into several groups viz. - Sweet Oranges, Sour Oranges, Grapefruits, Tangerines, Satsumas and Tangelos. Each of these groups have their own entry in the database.

Common Name: Sour Orange Group

General Information

Citrus aurantium is a much-branched evergreen tree with a rounded crown; it can grow from 3 - 10 metres tall[]. Young twigs bear slender short spines, whilst older branches have stout spines up to 8 cm long[].
The sour oranges are best known for their edible fruit, which is used to make marmalade, but the tree also has a range of other uses including medicinal applications, an essential oil and being grown as a hedge. The tree is often grown for its fruit in warm temperate to the tropical zones, important areas of cultivation are Paraguay, Morocco and Spain[].

Known Hazards

None known

Botanical References

Range

Tropical Asia?

Habitat

Original habitat is obscure, possibly a back cross involving C. maxima X C. reticulata[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	9.00 m
Pollinators	Apomictic, Insects
Self-fertile	Yes
Cultivation Status	Cultivated

Cultivation Details

Three main climates are suitable for commercial citrus production - tropical climates, subtropical with winter rain such as in the Mediterranean and semitropical with summer rainfall as found in Florida and southern Brazil[]. In the tropics, the plant grows best at elevations above 500 metres[], though elsewhere it grows best at an elevation below 300 metres, also succeeding up to 500 metres or perhaps a bit more[]. The optimal temperatures for citrus cultivation range between 25 - 30°c, with the coldest month having an average minimum of at least 15°c[]. Growth generally ceases below 13°c and above 38°c[]. This species can tolerate up to 45°c, provided soil moisture levels are adequate[]. The plant will be severely damaged, or killed by temperatures falling to -5°c or lower[]. An annual rainfall of 1,000mm falling mainly in spring and summer is the optimum, and irrigation is required where annual rainfall is below 750mm[]. If there are dry periods of more than three months, then irrigation will be necessary[].
Prefers a deep, well-drained but moisture-retentive loamy soil in full sun[]. Plants are intolerant of water logging[]. Prefers a pH in the range 6 - 7, tolerating 5.5 to 8.3[].
Plants dislike root disturbance and so should be placed into their permanent positions when young[].
Flowering of the bitter orange is strongly influenced by weather conditions. Bright, sunny and dry weather with mild temperatures is most suitable for flower production and harvesting[]. Cloudy, misty or hot and humid conditions reduce flower numbers and essential oil content[]. Bitter orange has a long life span; orchards 80-100 years old can still be productive[].

Edible Uses

Fruit - raw or cooked[, ]. Very acid and slightly bitter[]. The fruit is consumed fresh with salt and chilli in Mexico[]. It is widely used in making marmalade and other preserves[, , , ]. The immature fruits are eaten pickled in salt or vinegar as well as eaten fried in oil[]. The fruit is about 5 - 7cm in diameter[].

The rind of the fruit is often used as a flavouring in cakes etc[, ]. Used in 'bouquet garni'[].

An oil obtained from the seeds contains linolenic acid and is becoming more widely used as a food because of its ability to reduce levels of cholesterol in the blood[].

The flowers are used for scenting tea[].

An essential oil derived from the dried peel of immature fruits, and known as bitter orange oil, is used as a food flavouring for baked goods, chewing gum, ice cream, soft drinks and liqueurs[, ].

Petitgrain oil, an essential oil derived from the leaves, young branches and immature fruits, is used, like the bitter orange oil, for flavouring food products, drinks etc[].

Orange flower water is the condensed water remaining after neroli essential oil has been extracted from the flowers[]. This water was a common spice in former times[].

Medicinal

Citrus species contain a wide range of active ingredients and research is still underway in finding uses for them. They are rich in vitamin C, flavonoids, acids and volatile oils. They also contain coumarins such as bergapten which sensitizes the skin to sunlight. Bergapten is sometimes added to tanning preparations since it promotes pigmentation in the skin, though it can cause dermatitis or allergic responses in some people[]. Some of the plants more recent applications are as sources of anti-oxidants and chemical exfoliants in specialized cosmetics[]. The plants also contain umbelliferone, which is antifungal, as well as essential oils that are antifungal and antibacterial[]. They also contain the pyrone citrantin, which shows antifertility activity and was once used as a component of contraceptives[].

Both the leaves and the flowers are antispasmodic, digestive and sedative[, ]. An infusion is used in the treatment of stomach problems, sluggish digestion etc[].

The fruit is antiemetic, antitussive, carminative, diaphoretic, digestive and expectorant[].The immature fruit can be used (called Zhi Shi in China) or the mature fruit with seeds and endocarp removed (called Zhi Ke). The immature fruit has a stronger action. They are used in the treatment of dyspepsia, constipation, abdominal distension, stuffy sensation in the chest, prolapse of the uterus, rectum and stomach[].

The fruit peel is bitter, digestive and stomachic[].

The seed and the pericarp are used in the treatment of anorexia, chest pains, colds, coughs etc[].

The essential oil is used in aromatherapy. Its keyword is 'Radiance'[]. It is used in treating depression, tension and skin problems[].

Agroforestry Uses:

Grown as a hedging plant in N. America[].

Other Uses

This species is much used as a rootstock (especially for the sweet orange, lemon and grapefruit), because it produces a well-developed root system, has a high degree of disease resistance and greater hardiness[, , , ]. Its popularity has decreased, however, because of its susceptibility to the viral disease tristeza[].

A semi-drying oil obtained from the seed is used in soap making[, ].

Essential oils obtained from the peel, petals and leaves are used as a food flavouring and also in perfumery and medicines[, , , , ].
The oil obtained from the flowers is called 'Neroli oil', it is used in perfumery, soaps etc[]. Yields are very low from this species and so it is often adulterated with inferior oils[]. Neroli oil, mixed with vaseline, is used in India as a preventative against leeches[].
The oil from the leaves and young shoots is called 'petit-grain' - 400 kilos of plant material yield about 1 kilo of oil[]. This is also often adulterated with inferior products[].

The wood is strong and takes a fine polish. It is sometimes used to make furniture[].

Propagation

The seed is best sown in containers as soon as it is ripe, after thoroughly rinsing it[, ]. Sow stored seed in containers as soon as possible]. Germination usually takes place within 2 - 3 weeks at 13°c. Seedlings are liable to damp off so they must be watered with care and kept well ventilated. The seed is usually polyembryonic, two or more seedlings arise from each seed and they are genetically identical to the parent but they do not usually carry any virus that might be present in the parent plant[]. When large enough to handle, prick the seedlings out into individual pots and grow them on until they are 10cm or more tall before planting out into their permanent positions.
Cuttings of half-ripe wood, July/August in a frame. This species grows easily from cuttings[].
Layering in October.

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