Common name: Sweet acacia

Sweet acacia or Cashaw is a landscape and essential oil yielding shrub native to the Americas. Its natural range extends from the southern United States, through Central America and the Caribbean, to northern parts of South America. It is now widely introduced elsewhere and is cultivated in southern France for its flowers, which yield a valuable essential oil.

It may reach a height of up to 7 m (23 ft) in the wild but is more typically 3 to 5 m (10 to 16 ft) tall with multiple stems that lean away from the centre, forming a wide-spreading, V-shaped plant. The branches are slender with smooth, light brown bark and armed with sharp, needle-like thorns.

The leaves are small and consist of tiny leaflets in a feathery arrangement. Most are shed during the dry season to be replaced by new leaves in the rainy season.

The flowers are round like pom poms, yellow and sweetly fragrant. In most areas, they bloom from winter through spring and are followed by flat seedpods that turn dark brown or near black when mature, usually in late summer to autumn.

Use

Sweet acacia is occasionally cultivated as a barrier hedge because of its sharp thorns, and its ability to tolerate salt spray makes it particularly suitable for seaside gardens. It is used extensively in environmental plantings, including land reclamation projects, for its nitrogen-fixing capabilities and tolerance to drought and salt conditions.

The flowers yield an essential-oil absolute with a violet-like fragrance. Traded commercially as 'Cassie Ancienne', it is used in perfumes, confectionery and toiletry products.

The essential oil is extracted using a solvent. This is a low-temperature extraction process that preserves the delicate fragrance of the flower, which might otherwise be altered if steam distillation or other high-temperature extraction process is used. The resulting product is a waxy, yellow or brown mass that undergoes further refinement to produce the essential oil absolute, a yellow-brown, viscous fluid. Mature trees produce from 6 to 10 kilograms (13 to 22 lbs) of flowers per year, with 1 kg (2.2 lbs) yielding about 1 to 4 grams (0.04 to 0.14 ounces) of essential oil absolute.

The flowers do not produce much nectar, so they are of limited value to honey production but are a rich source of pollen for brood-rearing honeybees. 

The leaves and seedpods have a crude protein content of up to 17% of their dry weight. They are actively browsed by sheep and goats, making them an excellent livestock forage for dry areas.

The wood is hard and heavy, averaging about 830 kilograms per cubic meter (52 lbs per cubic ft), with high natural resistance to decay and rot. However, the roundwood comes mostly in small-diameter pieces suitable only for turnery and small poles and posts, cut from the main stems, especially fencing. It is widely harvested for firewood and for making charcoal.

Climate

Grows naturally in sub-humid subtropical and tropical lowland to high-elevation climates, generally in areas with annual lows of 11 to 25°C, annual highs of 20 to 35°C, annual rainfall of 300 to 1300 mm and a dry season of 4 to 8 months.

Growing

New plants are usually started from seed, which remain viable for years under proper storage conditions. The seed are treated before sowing by soaking them in boiling water that is left to cool. 

Performs best on sites with full to partial sun exposure, and on dry to moist, free-draining loam and sand soils of a moderately acid to alkaline nature, generally with a pH of 5.5.0 to 8.0. It has good tolerance to drought, salt and limestone soils but is intolerant of shade conditions.   

Problem features

The seed germinate readily after falling to the ground and can form dense thickets, especially where plants have escaped cultivation. Small livestock readily consume the seedpods and contribute to spreading the seed to new locations. It is reported as an invasive species in many countries and is assessed to be a high weed risk species by the Hawaii Pacific Weed Risk Assessment (HPWRA) project.

The branches are armed with sharp thorns that can inflict pain and injury on the unwary. The fallen seedpods produce a messy litter.  

Books

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

• Barwick, M., et al. 2004, Tropical & subtropical trees : a worldwide encyclopaedic guide, Thames and Hudson, London

• 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

• Chaplin, L. T. & Brandies M. M. 1998, The Florida Gardener's Book of Lists, Taylor Publishing Company, Dallas, Texas

• Dastur, J. F. 1964, Useful plants of India and Pakistan : a popular handbook of trees and plants of industrial, economic, and commercial utility, 2nd ed., D. B. Taraporevala Sons, Bombay

• Duke, J. A. 1983, Handbook of energy crops (unpublished), Center for New Crops & Plants Products, Purdue University, West Lafayette, Indiana

• Francis, J. K. 2004, Wildland shrubs of the United States and its territories: Thamnic descriptions, U.S. Department of Agriculture, Forest Service, International Institute of Tropical Forestry, Río Piedras, San Juan, Puerto Rico & Rocky Mountain Research Station, Fort Collins, Colorodo

• Francis, J. K. and Liogier, H. A. 1991, Naturalized exotic tree species in Puerto Rico, General technical report SO-82, USDA Forest Service, Southern Forest Experiment Station, New Orleans

• Francis, J. K. et al. 2000, Silvics of Native and Exotic Trees of Puerto Rico and the Caribbean Islands, Technical Report IITF-15, USDA Forest Service, Rio Piedras, Puerto Rico

• Gilman, E. F. 1997, Trees for urban and suburban landscapes, Delmar Publishers, Albany, New York

• Gohl, B. 1981, Tropical Feeds : feed information summaries and nutritive values (Revised edition), Food and Agriculture Organization of the United Nations (FAO), Rome

• Groom, N. 1997, The new perfume handbook, 2nd ed., Blackie Academic & Professional, London

• Hill, A. F. 1952, Economic botany : a textbook of useful plants and plant products, 2nd ed, McGraw-Hill, New York

• Howes, F. N. 1949, Vegetable gums and resins, Chronica Botanica Company, Waltham, Massachusetts

• Khan, I. A. & Abourashed, E. A. 2010, Leung's encyclopedia of common natural ingredients : used in food, drugs and cosmetics, 3rd edition, Wiley Publishing, Hoboken, New Jersey

• Krishen, P. 2006, Trees of Delhi : a field guide, Dorling Kindersley Publishers, Delhi

• Lawless, Julia 2013, The encyclopedia of essential oils : the complete guide to the use of aromatic oils in aromatherapy, herbalism, health, & well being, Conari Press, San Francisco, CA

• Macmillan, H. F. 1943, Tropical planting and gardening : with special reference to Ceylon, 5th ed, Macmillan Publishing, London

• National Research Council (Board on Science and Technology for International Development) 1979, Tropical legumes : resources for the future, The National Academies Press, Washington D. C.

• 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

• Perry, B. 2010, Landscape plants for California gardens: an illustrated reference of plants for California landscapes, Land Design Publishing, Claremont, California

• Sheikh M. I. 1993, Trees of Pakistan, USAID Forestry Planning and Development Project, Pictorial Printers, Islamabad

• Vázquez, Y. C. 1999, Potentially valuable Mexican trees for ecological restoration and reforestation, Institute of Ecology, Database SNIB-REMIB-CONABIO, Project J084, Mexico

• Webb, D. B. 1984, A Guide to species selection for tropical and sub-tropical plantations, 2nd ed., Unit of Tropical Silviculture, Commonwealth Forestry Institute, University of Oxford, Oxfordshire

Articles, Journals, Reports and Working Papers

• Meerow, A.W. 1996, Native Trees for South Florida, University of Florida-IFAS Publication EES-57, Gainesville

• Morton, J.F. 1964, Honeybee Plants of South Florida, Proceedings of the Florida State Horticultural Society, Vol 77:415-436.