Ocimum gratissimum

Common name: Clove basil

Other common names: African basil, African tea bush, Camphor basil, Clocimum, East Indian basil, Mary bush, Shrubby basil, Tree basil

Names in non-English languages: India

Description

Clove basil is a close relative of common Basil (Ocimum basilicum) and is an aromatic shrub yielding an essential-oil. Originating in Africa and the Indian subcontinent, its natural range extends from East Africa, through Madagascar and the Seychelles, to India, Sri Lanka and Bangladesh. Nowadays it is widely introduced and cultivated for its oil, mainly in Brazil, Tahiti and Indonesia. 

There are two oil-yielding types or varieties which are almost indistinguishable in appearance and have similar growing requirements. However, their essential-oils are quite different, one has an oil content high in thymol, the other high in eugenol. Thymol is commonly extracted from Thyme (Thymus vulgaris) or Ajwan (Trachyspermum ammi), whereas eugenol is extracted from Cloves (Syzygium aromaticum).

It is a much-branched perennial shrub 1 to 2 m (3 to 6 ft) tall with a woody base, on top of which grows strongly aromatic herbaceous foliage with an untidy, bushy or weedy appearance. The leaves are dull green, heart-shaped, toothed on the margins, finely haired on both surfaces and get their strong aroma from oil glands dotted on the upper surface.

The flowers are small or insignificant, white or green-yellow borne on erect flowering-spikes at the tips of the branches. They bloom in winter, which coincides with the dry season in its native range, and are soon followed by very small, roundish fruit, made up of four, dry, one-seeded nutlets.

Use

The herbage, including the leaves, soft stems and flowers yield on steam distillation an essential-oil that, depending on the variety, is high in thymol or eugenol. The primary use of these oils is as a substitute for thyme and clove oil.

Thymol is a dark yellow to orange-yellow or brown liquid with a spicy, medicinal, somewhat herbaceous aroma. The flavour is described as warm, slightly bitter and burning with a medicinal aftertaste. It is used as an ingredient in cold and cough syrups and as a disinfectant in ointments, mouthwashes and soaps.

Eugenol is a pale yellow to brownish-yellow liquid with a warm, spicy aroma reminiscent of cloves and with a sweetly woody, floral top note. It is widely used in the food, confectionery, pharmaceutical and perfume industries, particularly in flavouring food and candy. It is also used as an antiseptic in toothpaste. Vanillin, the substance that gives vanilla its flavour is synthesised from eugenol. 

The oils also contain small amounts of geraniol, a substance found in many plants with insect repellent activity and in its refined form, is used in quite a few commercial insect repellents.

Climate

Grows naturally and produces herbage with a high oil content in sub-humid to moderately humid subtropical and tropical climates, generally areas with annual lows of 17 to 25 °C, annual highs of 27 to 36 °C, annual rainfall of 700 to 2000 mm and a dry season of 2 to 7 months, extending to 10 months with irrigation. Although it also grows well in wetter climates with no dry season, the oil content of the herbage is relatively low and of poor quality.

Growing

New plants are usually started from seed which germinate readily. It grows on a wide range of soils but performs best on well-manured, free-draining loam, sandy-loam and loamy-sand soils of a moderately acid to moderately alkaline nature, generally with a pH of 6.0 to 8.0, and on sites with full sun exposure. It is intolerant of slow-draining or waterlogged soils and herbage grown under shade has a low oil content.

Crops in intensive systems are irrigated once or twice a week, depending on soil moisture levels, and the herbage is harvested three times a year. It is harvested in the early stages of flowering and all herbaceous parts above ground are taken, including the soft stems, leaves and flowers. The plants can be repeat-harvested for up to five years before they lose vigour and replanting becomes necessary.

In commercial operations, around 50,000 kilograms of fresh herbage is harvested, on average, per hectare, per year. And with an oil content of 0.3 to 0.6%, yields 150 to 300 kilograms of oil on distillation, the equivalent of 134 to 268 pounds of oil, per acre, per year.

Problem features

The seed are small and easily dispersed by wind and water. It is widely distributed and naturalised in the tropics, including parts of Africa, Central and South America and is a declared weed in multiple Caribbean and Pacific island nations.

Where it will grow

With irrigation or groundwater

References

Books

  • Adams, C. D. 1972, Flowering plants of Jamaica, University of the West Indies, Mona, Greater Kingston

  • Arctander, S. 1960, Perfume and flavor materials of natural origin, Elizabeth, New Jersey

  • Brady, G. S. & Clauser, H. R & Vaccari, J. A. 2002, Materials handbook : an encyclopedia for managers, technical professionals, purchasing and production managers, technicians and supervisors, 15th ed., McGraw-Hill, New York

  • Debboun, M. & Frances, S. P. & Strickman, D. 2006, Insect repellents : principles, methods, and uses, CRC Press, Boca Raton, Florida

  • Farooqi, A. A. & Sreeramu, B. S. 2004, Cultivation of medicinal and aromatic crops, Hyderabad University Press, Hyderabad

  • Guenther, E. & Althausen, D. 1948 to 1952, The essential oils (6 volumes), Van Nostrand Publishing, New York

  • Oyen, L. P. A. & Nguyen X. D. 1999, Plant Resources of South-East Asia (PROSEA) 19 : Essential-oil plants, Backhuys Publishers, Leiden

  • Parrotta, J. A. 2001, Healing plants of peninsular India, CABI Publishing, Wallingford, Oxfordshire

  • Randall, R. P. 2002, A global compendium of weeds, R.G. and F.J. Richardson Press, Melbourne

  • Seidemann, J. 2005, World spice plants: economic usage botany taxonomy, Springer-Verlag, Berlin

  • Space, J. C., et al. 2000, Invasive plant species on Kosrae : Federated states of Micronesia, USDA Forest Service, Institute of Pacific Islands Forestry, Hilo, Hawaii

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