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Leucaena

Contributor: James L. Brewbaker

Common Names
Scientific Names
Uses
Origin
Crop Status
Botany
1. Taxonomy
Crop Culture
Germplasm
1. Collections
Key References
Seleted Experts

Common Names

English: leucaena
Spanish: guaje
Native American: huaxin
Indian: subabul
Indonesian: lamtoro
Chinese: yin hue whan
Filipino: ipilipil
Pacific Island: tangantangan

Scientific Names

Species: Leucaena leucocephala (Lam.) de Wit
Family: Leguminosae
SubFamily: Mimosoideae

A multipurpose tree with extremely wide range of uses, based on naturalized and cultivated stands throughout tropics and subtropics. Uses of wood include fuelwood, lumber, pulpwood (paper, rayon), craftwood and charcoal. Uses of foliage include animal fodder, green manure and food (juvenile shoots). Feeding can be unrestricted to ruminant animals, but must be re-stricted to poultry and non-ruminants, where it is often used for its high contents of Vitamin A and protein. Uses of legumes and seeds include animal fodder, tea, medicinal and food (juvenile beans). Trees are used as ornamentals, windbreaks, shade trees, sources of green manure, and as stabilizing hedges on hillslopes. Gum is used as a substitute for gum arabic; seeds are strung into leis and jewelry; poles are used to prop bananas or crops like beans.

Origin

Mexico and Central America, origin obscured by wide distribution by man; Oaxaca translates "the place where huaxin (leucaena) grows."

Crop Status

Leucaena is international and found in many cropping and agroforestry schemes. It naturalizes weedily in some regions. All animals favor leucaena, one of the few woody tropical legumes that is highly digestible and relatively non-toxic. It is planted for intensive forage management in a few plantations in Queensland, Australia, and Texas, USA, and supplemented to grass pastures throughout the tropics in linear or block plantings. It is the most common leguminous shrub in alleycropping systems, often planted to stabilize sloping soils or provide green manure to crops like corn and millet. As a tree crop, leucaena is widely harvested for fuel and for pole and postwood. Improved varieties like K636 encourage efforts to harvest lumber and paperpulp on large plantation basis, with clear 30 cm boles on 14 m trees in 8 years. The wood is respected for charcoal and for furniture and craftwood in some countries. Leucaena foliage carries a mild toxin, the amino acid mimosine, that causes depilation in non-ruminant animals (e.g., horses). Contents range between 4 and 7 percent dry weight in foliage and in seeds. Mimosine degrades to dihydroxypyridines that can be goiterogenic, and these are further degraded in ruminant animals by the bacterium Synergistes jonesii. Animals lacking this bacterium are not uncommon in temperate regions or highland tropics, and can be introduced to the rumen. Non-ruminant animals must be fed leucaena in only limited amounts to avoid the mild toxicity symptoms. Some success is reported in using these toxins as fungicides or insecticides.

Botany

Taxonomy

Commercial use of leucaenas outside the New World is almost exclusively of the species Leucaena leucocephala (Lam.) de Wit, 2n=104. This is rapidly changing to include hybrids of this and other species, notably L. pallida Britton and Rose, 2n=104 and L. diversifolia (Schlecht) Benth., 2n=104 varieties. These three polyploid species intercross with ease. The latter two provide cold tolerance and L. pallida provides resistance to psyllid insect damage. The common worldwide leucaena is a single self-pollinated variety of L. leucocephala, the "common" cultivar, with virtually no genetic diversity outside of its center of origin. New cultivars are all of the arboreal or "giant" type, that greatly outyield the common in forage or wood and that are much less weedy. At least 13 other species are known in the genus, of which all but one are self-incompatible diploids (2n=52 or 56). About 90 interspecific hybrids have been produced artificially, many affording opportunities for further breeding and a few of immediate interest as seedless clones with high vegetative vigor. Lesser-known species with some commercial interest include L. collinsii, L. diversifolia (2n), L. diversifolia (4n), L. esculenta, L. pallida and L. pulverulenta. All leucaenas are woody perennials of the New World, ranging from Texas south to Ecuador, in dry and mesic secondary forests.

Crop Culture

Ecology

L. leucocephala is restricted to lowlands up to 1000 m elevation, but its interspecific hybrids greatly extend this range. Annual rainfall in the range of 650-1500 mm is typical, but leucaenas can be found in much drier or wetter sites depending on competing vegetation and drainage. Low tolerance of free aluminum and high calcium requirements contribute to leucaena's poor growth on soils under pH 5. Performance is excellent on coraline and other calcareous sites up to pH 8. Tolerance of saline soils is low, but it can be found on alkaline soils. It shows a wide range of tolerance to heat and desiccation, while growth is very poor under mean annual temperatures of 20°C and tolerance of severe frost is very low, although commercial production of forage occurs in some regions where mild frosts are common.

Cultivars

The 'common' cultivar is a naturalized shrub of Florida, Hawaii, Puerto Rico and of almost every tropical country and island, but is generally never to be recommended. Since 1960 the cultivars 'Cunningham', 'K8', 'K28' and 'K67' have become worldwide. Since 1990 the cultivar 'K636' and hybrids 'KX2' and 'KX3' have been widely distributed for improved yields and insect and cold tolerance.

Production Practices

Leucaenas are multipurpose trees that withstand almost any type or frequency of pruning or coppicing. Seeds must be scarified to improve germination, usually by immersion in hot water at 80°C for three minutes. Inoculation with rhizobia is recommended on many soils, although the rhizobia are almost universal in tropical soils. Improved strains include CB81 and TAL1145. Forage production is usually in rows 1-3 m apart with seeding rate of about 5-10 kg/ha (40,000 to 80,000 seeds), sown shallow and protected from weed competition at least three months. Produced for forage, they may be grazed as sole or inter-crops, or harvested by hand or machine at intervals ranging from six to 26 weeks. Tree plantations maximize yields between 5000 and 15000/ha, and are usually transplanted from nursery at age of 3-4 months. Dibble tubes 2 cm diameter, 15 cm long, with tapered open base are ideal for the strongly tap-rooted leucaenas. Seedlings may also be transplanted bare-root, rolled in mud, when soil moisture is adequate. Typical growth results in canopy closure in 4 to 6 months, during which weed control is essential.

Harvesting

Forage harvest is often by grazing animals on continuous or rotated pastures. Hand harvest is off of bushes pollarded to 75 cm height, leaving some foliage in lower canopy to ensure rapid regrowth. Foliage yields maximize when mean weekly increment falls to the level of overall average weekly yield, usually in about three months. Yields double when mean temperatures increase from 22°C to 32°C. Forage harvest should precede any flowering. Silage can be made, but foliage is normally fed fresh to ruminant animals. Foliage may be dried or pelleted for addition to poultry and non-ruminant rations up to 5% of diet. Poles may be harvested on almost any regime, from 6 months for bean poles to 3 years for banana props. Fuelwood and lumber harvests optimize with 3 to 8 year rotations when growth is not severely limited in some way. Trees coppice rapidly to 8 m in one year.

Processing

Leucaena forage can be ensiled, cubed or pelletized.

Germplasm

Collections

About 3000 accessions exist, including duplicates, in the following collections:

University of Hawaii, Dept. Horticulture, 3190 Maile Way, Honolulu, HI 96822

Oxford Forestry Institute, 5 S. Parks Rd., Oxford OX1 3RD, UK

Cunningham Lab, CSIRO, Brisbane, Qld., Australia

USDA South Central Regional Plant Introduction Station, Experiment, Georgia

International Livestock Center for Africa, Addis Ababa, Ethiopia

Key References

Brewbaker, J.L. 1987b. Leucaena: A multipurpose tree genus for tropical agroforestry. In Agroforestry: A Decade of Development, ed. H.A. Steppler & P.K.R. Nair, 289-323. Nairobi, Kenya: ICRAF.
Brewbaker, J.L. & Sorensson, C.T. 1990. New tree crops from interspecific Leucaena hybrids. In Advances in New Crops, ed. J. Janick et al., 283-289. Portland, Oregon: Timber Press.
Brewbaker, J.L. & Sorensson, C.T. 1994. Domestication of lesser-known species of the genus Leucaena. In "Tropical Trees; The Potential for Domestication and Rebuilding of Forest Resources", ed. R.R.B. Leakey and A.C. Newton, HMSO, London. pp.195-204.
National Research Council. 1984. Leucaena: Promising forage and tree crop for the tropics. 2nd ed. Washington, D.C.; US National Academy of Sciences.
Pound, B. and L. Martinez Cairo. 1983. Leucaena: Its cultivation and use. London: Overseas Development Administration.
Sorensson, C. T. and J. L. Brewbaker. 1994. Interspecific compatibility among 15 Leucaena species (Leguminosae: Mimosoideae) via artificial hybridizations. Amer. J. Bot. 81(2):240-247.

Seleted Experts

James L. Brewbaker, Dept. of Horticulture, University of Hawaii, 3190 Maile Way, Honolulu, HI 96822. Tel. 808-956-7985; Fax. 808-956-3894; E-mail; brewbake@uhunix.uhcc.hawaii.edu

Colin Hughes, Oxford Forestry Institute, 5 S. Parks Rd., Oxford OX1 3RD, UK. Tel. 44-864-275000, Fax 44-864-275074

H. Max Shelton, Dept. Agriculture, U. Queensland, Brisbane, Qld., Australia 4072. Tel. 61-7-3652651, Fax 61-7-3651188

Contributor: James L. Brewbaker, Dept. Horticulture, University of Hawaii

Last update Tuesday, February 24, 1998 by aw