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18: Plants producing exudates

Hymenaea courbaril L.

Sp. pl.: 1192 (1753).

LEGUMINOSAE

2n = 24

Hymenaea candolleana Kunth (1823), Hymenaea retusa Willd. ex Hayne (1830), Inga megacarpa M.E.Jones (1929).

West Indian locust, jatoba, courbaril (En). Indonesia: kobari, locus (general). Philippines: jatoba.

Hymenaea courbaril is native to the American tropics and is distributed in the West Indies, and in Central and South America from southern Mexico to Brazil. It is cultivated in the tropics, was introduced into Singapore in 1875 and is now found in Malesia, particularly in Peninsular Malaysia, Sabah and Java.

All parts of Hymenaea courbaril contain a resin, but it is generally only tapped from the bark. The resin is used in special grades of varnishes, lacquers, paints, inks, plastics, sizing, adhesives, fireworks, and crockery cements. It is used to a lesser extent as incense and for medicinal purposes and for patent leather. Commercially the resin is known as 'South American copal'. In Brazil, it is the main source of the resin known as 'jatoba', 'jutaicica', 'jutai' or 'jutai-acu'.
The wood of Hymenaea courbaril is valuable and resembles mahogany (Swietenia Jacq.). It is hard and strong and used for construction, door and window frames, ship building, furniture, panelling and parquet flooring. The mealy pulp around the seeds is sometimes eaten by children, but it has an unpleasant smell. In Brazil, the fruit pulp is also used as a carbohydrate source in making alcoholic beverages for domestic consumption. The bark is a source of tannin and is so thick that it has been used by Indians to make canoes. In agroforestry it is employed as a nitrogen-fixing tree to rehabilitate degraded and marginal soils. It has also been planted as an ornamental tree, but its hard, heavy and malodorous fruits make it less suitable for this purpose. The flowers are attractive to bees and are used for honey production.

Brazil is the main source of the resin but international trade is believed to be very small or negligible. From 1976 to 1986 production in Brazil declined from 38 t to 23 t and the unit price also declined. No production data are available from South-East Asia. 'Recent copal', obtained by tapping, is sent to India and China, where it is manufactured into a coarse varnish.

South American copal varies in colour from an almost colourless transparent mass to bright yellow-brown. It usually has a dull, rough outer surface where it has suffered oxidation. The resin contains a relatively large amount of tannin. It also contains about 13% copalic acid, a cyclic diterpene. The quality and hardness of the resin are likely to increase with age. It is probably inferior to 'East African copal' (Hymenaea verrucosa Gaertn., Copaifera spp.) and 'East Indian copal' (Agathis borneensis Warb.).
The heavy heartwood is red-brown, streaked, with a density of 730 kg/m³ at 15% moisture content for an Indonesian sample, and 880—1000 kg/m³ for South-American samples. The wood hardly shrinks or warps. It is very hard, very strong and very tough. It is difficult to work, but planes, turns and polishes well.

An evergreen, medium-sized tree up to 25(—40) m tall, bole 1 m or more in diameter, often much smaller in cultivation; bark smooth, becoming 2.5 cm or more thick, grey to pinkish-brown. Leaves alternate, bifoliolate, glossy green above, gland-dotted; petiole 1—2 cm long, petiolules twisted, 2—4 mm long; leaflet blade falcate, rarely oblong or obovate, 4—10 cm x 2—5 cm, coriaceous, base asymmetrical and rounded, margin entire, apex short to long acuminate. Inflorescence terminal, densely corymbose-paniculate, 8—15 cm long and wide; pedicel 6 mm long. Flowers large, buds up to 3.5 cm long, open flower 3 cm in diameter, all parts glandular punctate; calyx campanulate, 4-merous, grey-green, tube (hypanthium) 6 mm long, lobes ovate to elliptical, 15—18 mm x 8 mm, imbricate, coriaceous, pubescent outside, sericeous inside; petals 5, subequal, oblong, ovate or obovate, equalling the calyx lobes or slightly longer, not clawed, yellow, streaked with red; stamens 10, 3.5 cm long, free, filaments white, folded in bud, anthers red, dorsifixed; pistil with stipitate ovary, stipe 4—8 mm long, ovary with about 15 ovules, style slender, curved about 2.5 cm long. Fruit a compressed cylindrical pod, 8—20 cm x 4—8 cm, smooth or rough but not rugose, dark brown, indehiscent and often remaining for a long time on the tree, usually with 6—12 seeds embedded in pale yellow, unpleasant smelling fruit flesh. Seed flattened ellipsoidal, 2—3 cm long, dark red. Seedling with epigeal germination.

Hymenaea courbaril develops according to the architectural model of Troll which is characterized by all axes being plagiotropic and is built by continuous superposition of branches thus forming a sympodial stem. Planted seedlings lack a leading shoot; they branch heavily, but will eventually form a clear bole. Young trees have a taproot, but later the root system spreads shallowly. In the Philippines, large nodules with a rough surface have been observed on the roots. In plantation trials in Peninsular Malaysia, trees attained 14 m height and 19 cm diameter in 8 years in the open. In trials in Java on fertile soil, Hymenaea courbaril had attained an average height of 20 m and an average diameter of 19—22 cm 10 years after planting. On moderately fertile soils trees also grow well. Fruiting is almost annual. In Singapore flowering starts in June and fruits need 10—11 months to ripen. In East Java Hymenaea courbaril flowers in November—April and ripe fruits are found in July—September. There are 280—300 dry seeds/kg as determined from trees grown in Indonesia; in India 800—900 dry seeds/kg have been counted. Dispersal of the seeds in Costa Rica is by agoutis (Dasyprocta punctata), a kind of rodent.

Within Hymenaea courbaril 6 varieties have been distinguished, of which 5 occur only in Brazil. Var. courbaril (described here) has a wide distribution in the American tropics and is also cultivated in the tropics of Africa and Asia, including South-East Asia.
Hymenaea verrucosa Gaertn. (synonym: Trachylobium verrucosum (Gaertn.) Oliv.) is a resin-producing species from tropical Africa which is also cultivated pantropically. Major differences with Hymenaea courbaril are: inflorescence up to 35 cm long, flowers small, buds less than 15 mm long, petals distinctly clawed, pod surface verrucose-rugose. See also the chapter on minor species.

Hymenaea courbaril is a light-demanding species and in South America it is found in secondary forest on sandy, well-drained soils. It mainly occurs in dry forests at low altitudes, although it can grow well at higher elevations.

Seed of Hymenaea courbaril can be stored for a long time without losing viability but should be scarified before sowing either by filing the seed coat, or by treatment with hot water or with concentrated sulphuric acid. In an experiment in India 70—80% germination was obtained after treatment with hot water or with concentrated sulphuric acid for 5—25 minutes whereas untreated seed did not germinate. In Costa Rica, seeds germinate well under natural conditions at temperatures above 23°C and in humid soil. Stripped seedlings or stumps can be used as planting stock giving a satisfactory survival, whereas direct seeding has also been used.
Planting trials on degraded land in West Java (Indonesia) were not very successful, with only 9% survival after 2 years in one site and 68% survival after 8 months in another. On fertile soil, trials were more successful. A spacing of 3 m x 2 m was applied, but because of the heavy branching 3 m x 1 m has been recommended.

Hymenaea courbaril has never been planted for its resin. For timber production the young trees need strong lateral competition because of the weak apical dominance. Even large branches are readily shed.

No particular diseases or pests have been observed in Hymenaea courbaril in South-East Asia. In South America several pathogens have been identified, but their importance is probably minor.

In South America trees of Hymenaea courbaril used to be tapped. The fresh resin obtained by tapping the trees ('recent copal') is much softer than that dug up from the ground ('fossil copal'). It has the nature of a balsam or soft elemi and is also used medicinally. The pale yellow or reddish resin exudes from the bark and trickles to the ground where it hardens into lumps and eventually become covered with soil. In the course of time considerable quantities of resin collect in this way.

Native collectors in South America can obtain a barrel full of resin of Hymenaea courbaril by digging around the roots of a tree, and several barrels from the former site of a large tree that has long since decayed. In a 60-year-old trial plantation in Peninsular Malaysia a mean annual volume increment of 3.7 m³/ha was obtained and 3 m³/ha was produced in East Java by an 11-year-old trial plantation.

The resin of Hymenaea courbaril is not processed further and is used directly for the manufacture of varnishes and lacquers.

There are no known germplasm collections or breeding programmes for Hymenaea courbaril. It is not threatened by extinction.

Hymenaea courbaril is more important for timber production than for its resin; its fairly fast growth and good wood quality may hold promise for the future. The prospects for the resin market, however, are not promising.

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Widiarti, A. & Alrasjid, H., 1987. Penanaman introduksi jenis pohon kayu bakar di lahan kritis Paseh dan Kadipaten [Introduction of fuelwood tree species on degraded lands in Paseh and Kadipaten areas]. Buletin Penelitian Hutan 488: 1—17.

N.O. Aguilar

Aguilar, N.O., 2000. Hymenaea courbaril L.. In: Boer, E. and Ella, A.B. (Editors): Plant Resources of South-East Asia No 18: Plants producing exudates. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea