Samanea saman (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Samanea saman (Jacq.) Merrill

Protologue: J. Wash. Acad. Sci. 6: 47 (1916).

Family: Leguminosae - Mimosoideae

Chromosome number: 2n= 26, 14 also reported

Synonyms

• Mimosa saman Jacq. (1800-1809),
• Pithecellobium saman (Jacq.) Benth. (1844),
• Enterolobium saman (Jacq.) Prain (1897).

Vernacular names

• Rain tree, monkeypod, cow tamarind (En).
• Arbre de pluie, saman, zamang (Fr)
• Indonesia: trembesi, kayudan (Javanese), ki hujan (Sundanese)
• Malaysia: hujan-hujan, pukul lima (Peninsular Malaysia)
• Philippines: acacia
• Cambodia: 'âmpül barang'
• Laos: (do:k) sa:m sa:
• Thailand: kampu, chamchuri (central), chamcha (northern)
• Vietnam: me tây.

Origin and geographic distribution

S. saman is a native of northern tropical South America. It is now cultivated and naturalized throughout the tropics, including South-East Asia.

Uses

S. saman is commonly grown as a shade tree and as ornamental. It has been planted as a shade tree in cocoa, coffee, vanilla, and in young nutmeg and teak plantations. It can be used as a hedge tree, if lopped heavily. In north-eastern Thailand, mature trees are highly valued as a host for the lac insect (Laccifer lacca). Green leaves of S. saman are a high quality feed for sheep, goats and cattle and are used as a supplement during the dry season. The sweet pods are nutritious and relished by ruminants and pigs, who also take advantage of the shade provided in pastures. Because of its prolific flowering, S. saman is also profitable for honey production.

The wood, which is not durable, produces a high quality timber for carving, furniture and panelling. It provides a good quality firewood and charcoal, although it produces much smoke, even when very dry. Where a market for wood carvings exists, it is too valuable to be used as firewood.

Production and international trade

The production and trade of S. saman is mainly local and no statistics are available. The famous "monkeypod" bowls from Hawaii are made of S. saman wood. As the wood is getting scarce, it is now imported in considerable quantities from Indonesia and the Philippines.

Properties

Per 100 g dry matter the leaves and twigs of S. saman contain 22-27 g crude protein and 44-53 g neutral detergent fibre, the pods and seeds 12-18 g and 38 g respectively. The in vitro digestibility of the leaves is 58-68%, that of the pods is 40%. The mineral content of leaf litter per 100 g dry matter is: N 2.0 g, P 0.3 g, K 0.15 g, Ca 1.16 g, and Mg 0.01 g. Firewood has an energy value of 25 000-27 000 kJ/kg.

Dry leaves have the heavy scent of coumarin, reminiscent of newly mown hay. The bark lacks tannins, but yields an inferior gum. The bark and seeds contain a minor, saponin-like alkaloid, pithecolobine.

The heartwood of S. saman is dark walnut to dark chocolate-brown, turning to light brown or golden-brown with darker streaks when seasoned. The sapwood is whitish. The wood has a basic density at 12% moisture content of 550-700 kg/m³and is strong and hard. Shrinkage is extremely low and green wood can be carved out without risk of warping or splitting. It is resistant to dry wood termites.

The weight of 1000 seeds is 125-225 g.

Description

• A large, evergreen, unarmed tree, up to 25(-40) m tall at maturity with a trunk diameter at breast height up to 2 m, with wide-spreading crown up to 25-30 m in diameter. Bark finely fissured, light grey to greyish-brown. Branchlets puberulous to tomentose.
• Leaves bipinnate, not sensitive to the touch; stipules lanceolate, small, not spinescent, caducous; rachis up to 40 cm long; pinnae 3-9 pairs, up to 11 cm long; concave circular glands present just below the basal pair of pinnae, between all other pairs of pinnae, and at the junction of the leaflets; leaflets opposite, 2-10 pairs per pinna, oblique-ovate to elliptical or subrhomboid, 1.5-6 cm × 0.7-4 cm, apex obtuse-rounded, often emarginate, mucronate, base asymmetrical, upper surface glabrous, lower surface densely short pubescent, main vein diagonal, lateral veins forming a prominent, dense reticulate pattern.
• Inflorescence a corymb, 2-5 together in the axils of distal leaves; peduncle erect, 5-10 cm long, densely, shortly, yellowish pubescent; corymb with dimorphic flowers, consisting of a larger, 7-8-merous central flower, surrounded by smaller 5-merous marginal flowers.
• Central flower up to 2.5 cm long, sessile, calyx broadly cylindrical, 8-9 mm × 4-5 mm, corolla up to 12 mm long, staminal tube longer than the corolla; marginal flowers up to 3.5 cm long, on short (3 mm) pedicels, calyx funnel-shaped, 5-7 mm long, tomentose or woolly, teeth broadly triangular, acute, 0.5-1 mm long, corolla funnel-shaped, about 10-12 mm long, distal part tomentose or woolly, red or yellowish-red, lobes triangular-ovate, about 2 mm long, stamens 20-35 mm long, white at the base, purple toward the top, tube shorter than corolla tube.
• Pod oblongoid, straight or slightly curved, 15-20 cm × 1.5-2.3 cm, turgid with thickened margins, indehiscent, woody, black, about 15-seeded; crustaceous exocarp loosens from the pulpy, sweet mesocarp; endocarp woody, forming one-seeded chambers.
• Seed ellipsoid, strongly biconvex, 9 mm × 5 mm × 4 mm, brown with a distinct U-shaped pleurogram, shiny, not arillate, areole elliptical, 7 mm × 3 mm.
• Seedling with epigeal germination.

Growth and development

S. saman grows slowly in the first year of planting, but is generally considered to be fast growing. The first two leaves are opposite or sub-opposite, subsequent leaves are arranged spirally. In Thailand, trees reached a height of 1.3 m, 11 months after planting, whereas in Indonesia the height increment was 0.7 m and the diameter increment 1.5 cm in the first 6 months after planting. On average planted stumps reached a height of 2 m, 7.5 months after planting. In a trial plantation in Papua New Guinea, S. saman planted at 2 m × 3 m distance attained an average height of 2.3 m and a diameter of 4.5 cm, 8 months after planting. Young trees often shed their leaves during the dry season.

In Thailand, mature trees flower twice a year, in February-May and in September-November. In Java, flowering is observed from August to April. Fruits mature 5.5-8 months after flowering.

S. saman forms N-fixing nodules with strains of Bradyrhizobium. In the Philippines, S. saman proved highly responsive to inoculation with vesicular-arbuscular mycorrhizae and the increase in biomass was 40% compared with uninoculated plants.

The abundance of epiphytic ferns and orchids on avenue rain trees, as observed in Peninsular Malaysia, is a striking phenomenon. The trees tend to have a large crown with wide-spreading branches and their branches can stretch right across roads. This habit, however, makes the tree unsuitable for smallholder woodlots.

Other botanical information

The genus Samanea Merrill is closely related to Albizia Durazz. and distinction between the two genera is difficult. Some differences are: Samanea : central flower with 7-8 perianth segments (Albizia 5), fruits fleshy and internally segmented (Albizia fruits are not fleshy and usually not segmented inside). A thorough revision of the 2 genera might reveal that they should be united.

At night and during cloudy days the leaves of S. saman droop. The extrafloral nectaries excrete sugar-rich juice which sometimes drops from the tree like rain (hence rain tree). At flowering time abundant stamens drop like a shower from the tree canopy from time to time.

Ecology

S. saman thrives in a wide range of climatic and soil conditions, from sea level up to 1000 m altitude. It is found in both monsoon and equatorial climates with an annual rainfall of 1000-2500 mm. It is not well adapted to climates with a pronounced dry season and withstands only 2-4 dry months. A lower rainfall (700 mm) is tolerated if evenly distributed throughout the year, as in Curaçao. It grows best in climates with a mean minimum temperature of the coldest month of 18-22 °C and a mean maximum temperature of the hottest month of 24-30 °C. S. saman is rarely found in forest stands and requires high light intensities.

Soil requirements range from moderately acidic to alkaline, pH 5.5-8.5. It grows well on clayey or sandy soils and withstands seasonal waterlogging.

Propagation and planting

S. saman is commonly propagated by seed, but can also be propagated through stem and root cuttings. Pods can be collected from the ground. If left in a dark place, the valves are eaten by termites, while the clean seeds are left intact. Mature seed has a hard seed-coat and must be treated for even germination. To break dormancy the seed is immersed in hot water for 3 minutes and then soaked overnight in cool water. Passage through the intestines of herbivores also enhances germination. Germination of untreated seed increases in the course of the first year of storage. Seed sown in containers placed in full light generally have a germination rate of over 90%. Seedlings can be planted in the field after 6-8 weeks when they are 15-25 cm tall. They may be stumped with a root length of 40 cm, a shoot length of 20 cm, and a diameter of 0.5-3 cm. When grown for fodder, seedlings are spaced at 3 m × 1 m. Spacings of 4 m × 4-8 m are recommended for wood production. In the Philippines, S. saman is planted at 10 m × 10 m spacing in coffee plantations grown at 3 m × 3 m.

Husbandry

S. saman planted on paddy bunds in north-eastern Thailand increased the organic matter content of the topsoil from 0.36% to 0.58% and the total soil nitrogen from 0.06% to 0.08%, while the pH increased from 4.8 to 5.8 under the trees. However, shading also caused a reduction in the yield of rice. In Malaysia, an increase in growth, yield and nutritive quality of the pasture grass Axonopus compressus (Schwartz) P. Beauv. was observed when grown under S. saman. This is attributed to the higher N content of the soil and a beneficial micro-climate under the trees. Folding of the leaves and drooping branches allow rainfall to reach the grass directly during the night and on cloudy days (another reason for the name rain tree). On sunny days, the unfolded leaves provide shade and help to conserve moisture.

When planted in hedges trees should be maintained by heavy lopping. In north-eastern Thailand, S. saman is pollarded at 1 m height every six months for the production of fodder. Pollarding is also used for firewood production.

For lac production in north-eastern Thailand, lac insects are usually cultured on the trees during December and February. The lac can be harvested 12 months later. After harvesting, the trees are left uncut for at least 3 years before restarting the lac cultivation.

Diseases and pests

A wound parasite, Ganoderma lucidum is reported from the Philippines. It may cause white soft rot in the lower part of the stem. A powdery mildew (Erysiphe communis) is very common in nurseries and may cause complete defoliation of seedlings. Two psyllid species attack S. saman, but rarely cause serious damage. The leucaena psyllid (Heteropsylla cubana) feeds on young shoots and in severe cases may cause defoliation, stunted shoot growth and eventually the death of the tree. Psylla acacia-baileyanae feeds on the shoots, causing leaves and shoots ots to curl.

Yield

Annual increment of wood is 10-15 m³/ha when harvested 10-15-years after planting. Yields of lac depend on tree size, but annual amounts of 50-100 kg per tree have been obtained.

Genetic resources and breeding

Neither substantial germplasm collections nor breeding programmes of S. saman are known to exist.

Prospects

S. saman is a valuable multipurpose tree. It is easily raised and can grow under a wide range of environmental conditions. The slow initial growth is a disadvantage for wood or fodder production. The integration of lac production with firewood and timber production warrants further studies.

Literature

• Akkasaeng, R., Gutteridge, R.C. & Wanapat, M., 1989. Evaluation of trees and shrubs for forage and firewood in north-east Thailand. The International Tree Crops Journal 5: 209-220.
• Gutteridge, R.C., 1990. Agronomic evaluation of tree and shrub species in South-East Queensland. Tropical Grasslands 24: 29-34.
• Nielsen, I.C., 1992. Mimosaceae (Leguminosae - Mimosoideae). In: de Wilde, W.J.J.O., Nooteboom, H.P. & Kalkman, C. (Editors): Flora Malesiana, Series 1, Vol. 11(1). Foundation Flora Malesiana, Leiden University, Leiden, the Netherlands. pp. 155-156.
• Nitrogen Fixing Tree Association, 1987. The multi-purpose rain tree, Samanea saman. NFTA, Waimanalo, Hawaii, United States. 2 pp.
• Quiniones, S.S. & Dayan, M.P., 1981. Notes on the diseases of forest species in the Philippines. Sylvatrop 6: 61-67.
• Relwani, L.L., Lahane, B.N. & Gandhe, A.M., 1988. Performance of nitrogen-fixing MPTS on mountainous wasteland in low rainfall areas. In: Whithington, D., MacDicken, K.G., Sastry, C.B. & Adams, N.R. (Editors): Multipurpose tree species for small farm use. Winrock International Institute for Agriculture Development and International Development Research Center of Canada. pp. 105-113.
• Sae-Lee, S., 1990. Effect of trees in rice paddies on soil fertility and rice growth. MSc.-thesis in Soil Science, Graduate School, Khon Kaen University, Khon Kaen, Thailand. 172 pp. [in Thai with English abstract].
• Zhou, X.Q. & Han, S.F., 1984. Studies on symbiotic system of nodule bacteria and tree legumes. 1. Nodulation, isolation, and reciprocal cross inoculation. Journal of Nanjing Institute of Forestry 2: 32-42.

Authors

R. Akkasaeng