Common name: Diesel tree

Diesel tree is a resin-yielding tree legume native to South America, where it occurs in Brazil, mostly in the south-east of the country and to a lesser extent in scattered distributions in the central-east and north-east.

It is a medium-sized tree, typically 10 to 15 m (32 to 50 ft) tall. On open sites, it develops a stout trunk supporting a densely leafy rounded crown. The bark is pale grey-brown and smooth, becoming dark brown and rough with age.

Leaves are large, 50 to 80 cm (1.6 to 2.6 ft) long and feathery, consisting of six to ten dark green oval leaflets, each 4 to 5 cm (1.6 to 2 in) long and arranged in pairs along the length. In the dry season, they fall off the tree to conserve water, leaving the branches bare or partially bare until the rainy season, when the new leaves emerge. 

The flowers are small and without petals but have four white sepals borne in clusters arising at the sides of the branches. They bloom in the rainy season, which coincides with summer in its native range, and are followed by small flattened egg-shaped seed capsules, 2.8 to 3.5 cm (1 to 1.4 in) long. The seed capsules mature in the dry season, becoming pale brown when the tree is near leafless. They contain a single large black seed partially covered with a thick, fleshy, bright yellow to reddish aril.

Use

The bark, on wounding, yields a thick, yellowish oleoresin (oily resin), tapped by making V-shaped incisions in the bark or by boring long canals up to the start of the heartwood. Traded as 'Copaiba oil', it is used mainly for medicinal purposes and to make varnishes.

Copaiba oil has recently received interest as a biofuel for producing biodiesel, partly because it needs little refinement to convert it to engine fuel. Individual trees reportedly yield up to 40 litres (10 gallons) of oleoresin per year. However, recent scientific studies have found the yields to be considerably lower.

The wood is medium-weight, averaging 700 kgs per cubic meter (44 lbs per cubic ft), and is moderately resistant to decay and wood-boring insects. The heartwood is variable, golden- to reddish-brown with dark streaking that can be worked to a smooth, lustrous finish. It is used mostly for house construction, furniture and cabinets, interior joinery, including doors and window frames, interior flooring, and turnery for making handles of various kinds.

It is sometimes planted as an amenity tree for its shapely form and to provide shade from the sun.

Health use

Copaiba oil is used in medicinal preparations against inflammatory conditions, particularly of the bladder and urethra, and to loosen mucus in the respiratory tract. It is also reported as an effective topical treatment against eczema and other skin diseases. It is the oil rather than the resin that is the active constituent.

Climate

Grows naturally in moderately humid subtropical and tropical climates, generally in areas with annual lows of 13 to 20°C, annual highs of 25 to 35°C, annual rainfall of 700 to 2000 mm and a dry season of 7 months or less

Growing

New plants are usually started from seed. The seed capsules are harvested when they begin to split open and are then left in the sun to dry. After drying, the seed are extracted and sown in containers with a free-draining potting mix. Most seed germinate within twenty to forty days.

Performs best on deep, free-draining clay, loam and sand soils of an acid to neutral nature, generally with a pH of 4.5 to 7.5, and on sites with full to partial sun exposure.

Problem features

It has been relatively uncommon in cultivation until recent times, and hence its invasive capacity is largely unknown. However, the tree produces a large amount of fruit, and birds feed on the arils, and in so doing, facilitate seed dispersal. An assessment by the Hawaii Pacific Weed Risk Assessment (HPWRA) project has not found it to be a high weed risk for Hawaii. However, a reassessment is pending.

Copaiba oil is toxic in overdose and should only be used under professional medical supervision.

Books

• Allen, O. N. & Allen, E. K. 1981, The Leguminosae : a source book of characteristics, uses, and nodulation, University of Wisconsin Press, Madison, Wisconsin

• Chevallier, A. 2000, Encyclopedia of herbal medicine, 2nd American ed., Dorling Kindersley, New York

• Coppen, J. J. W. 1995, Gums, resins and latexes of plant origin, Food and Agriculture Organization of the United Nations (FAO), Rome

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

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

• Lorenzi, H. 2002, Brazilian trees : a guide to the identification and cultivation of Brazilian native trees. Vol. 1, 4. ed, Instituto Plantarum de Estudos da Flora, Nova Odessa, Sao Paulo

• Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

• Shanley, P. 2002, Tapping the green market : certification and management of non-timber forest products, Earthscan Publishing, London

• Winter, R. 2009, A consumer's dictionary of cosmetic ingredients : complete information about the harmful and desirable ingredients found in cosmetics and cosmeceuticals, 7th ed, Three Rivers Press, New York

Articles, Journals, Reports and Working Papers

• Buddenhagen C.E., Chimera C. & Clifford P. 2009, Assessing Biofuel Crop Invasiveness: A Case Study, PLoS ONE 4