Leucaena leucocephala (leucaena)

Pictures

Picture	Title	Caption	Copyright
Title Fenceline tree Caption L. leucocephala subsp. glabrata habit: fenceline tree to 10m tall, Comayagua, Honduras. Copyright Colin Hughes, Dept. Plant Sciences, Univ. Oxford	Fenceline tree	L. leucocephala subsp. glabrata habit: fenceline tree to 10m tall, Comayagua, Honduras.	Colin Hughes, Dept. Plant Sciences, Univ. Oxford
Title Foliage, flowers and seed pods Caption L. leucocephala foliage, flowers and seed pods. Copyright N.M. Pasiecznik	Foliage, flowers and seed pods	L. leucocephala foliage, flowers and seed pods.	N.M. Pasiecznik
Title Flower and flower buds Caption L. leucocephala subsp. glabrata open flower head and unopened flower buds. Copyright Colin Hughes, Dept. Plant Sciences, Univ. Oxford	Flower and flower buds	L. leucocephala subsp. glabrata open flower head and unopened flower buds.	Colin Hughes, Dept. Plant Sciences, Univ. Oxford
Title Seed pods Caption L. leucocephala subsp. glabrata cluster of unripe pods on a single flower head; heavy pod and seed set is often attributed to self-fertility. Copyright Colin Hughes, Dept. Plant Sciences, Univ. Oxford	Seed pods	L. leucocephala subsp. glabrata cluster of unripe pods on a single flower head; heavy pod and seed set is often attributed to self-fertility.	Colin Hughes, Dept. Plant Sciences, Univ. Oxford
Title On terrace boundaries Caption L. leucocephala subsp. glabrata cultivated on terrace boundaries, Choluteca, Honduras. Copyright Colin Hughes, Dept. Plant Sciences, Univ. Oxford	On terrace boundaries	L. leucocephala subsp. glabrata cultivated on terrace boundaries, Choluteca, Honduras.	Colin Hughes, Dept. Plant Sciences, Univ. Oxford
Title Pasture system Caption L. leucocephala subsp. glabrata cultivated for livestock feed in hedgerows in large-scale pasture systems, Queensland, Australia. Copyright H.M. Shelton, Univ. Queensland	Pasture system	L. leucocephala subsp. glabrata cultivated for livestock feed in hedgerows in large-scale pasture systems, Queensland, Australia.	H.M. Shelton, Univ. Queensland
Title Large scale cultivation Caption L. leucocephala subsp. glabrata: large scale cultivation for livestock feed with irrigation, Ord River, Northern Territories, Australia. Copyright H.M. Shelton, Univ. Queensland	Large scale cultivation	L. leucocephala subsp. glabrata: large scale cultivation for livestock feed with irrigation, Ord River, Northern Territories, Australia.	H.M. Shelton, Univ. Queensland
Title L. leucocephala - colour illustration Caption Leucaena leucocephala Copyright ©Wilhelm Valder	L. leucocephala - colour illustration	Leucaena leucocephala	©Wilhelm Valder
Title Intercropping with wheat Caption L. leucocephala subsp. glabrata alley farming with winter wheat intercrop, Jhansi, India. Copyright Colin Hughes, Dept. Plant Sciences, Univ. Oxford	Intercropping with wheat	L. leucocephala subsp. glabrata alley farming with winter wheat intercrop, Jhansi, India.	Colin Hughes, Dept. Plant Sciences, Univ. Oxford
Title Line artwork Caption Flowering and fruiting branch. Copyright PROSEA Foundation	Line artwork	Flowering and fruiting branch.	PROSEA Foundation

Identity

Preferred Scientific Name

• Leucaena leucocephala (Lam.) de Wit

Preferred Common Name

• leucaena

Subspecies

• Leucaena leucocephala subsp. glabrata

Other Scientific Names

• Acacia frondosa Willd.
• Acacia glauca (L.) Willd.
• Acacia leucocephala (Lam.) Link
• Acacia leucophala Link
• Leucaena glabra Benth.
• Leucaena glauca Benth.
• Leucaena latisiliqua (L.) Gillis
• Mimosa leucocephala Lam
• Mimosa leucophala Lam.

International Common Names

• English: coffee bush; false koa; hedge acacia; horse tamarind; ipel-ipel; ipil-ipil; jumbie-bean; jumpy-bean; lead tree; white popinac; wild tamarind
• Spanish: acacia bella rosa; acacia pálida; campeche; chamba; guaje; hediondilla; huaxin; peladera; tamarindo silvestre; uaxim; zarcilla
• French: cassi; faux acacia; faux mimosa; graines de lin; grains de lin pays; l'acacie; leucaene; mimosa; tamarin batard; tamarin cheval
• Chinese: yin he huan

Local Common Names

• Australia: cow tamarind; jumbie bean; leadtree; white leadtree
• Bahamas: jumby bean
• Belize: wild tamarind
• Brazil: faux-acacia
• Cambodia: kanthum theet; kratin
• Cook Islands: marainu; mara'inu; nito
• Cuba: aroma blanca; aroma boba; aroma boba; aroma mansa; aroma mansa; soplillo; soplillo
• Dominican Republic: granadillo; granalino; Grenadillo bobo; lino; lino criollo
• El Salvador: barba de leon
• Fiji: balori; vaivai; vaivai dina; vaivai ni vavalangi
• Guam: tangan-tangan
• Guatemala: chalip; guash criollo
• Haiti: delen; lisina; tchia-tchia marron
• Hawaii: ekoa; false koa; haole koa; koa-haole; lilikoa
• Honduras: frijol guaje
• India: kubabul; lasobayal; nattucvundal; subabool; subabul; tagari; vilayati baral
• Indonesia: lamtoro; lamtoro gung; petai cina
• Java: klandingan
• Kiribati: te kaitetua
• Laos: kathin; kh'oonz; koong khaaw
• Lesser Antilles: macata; macta-bourse; monval; tamarin bâtard; wild mimosa; wild tamarin
• Malaysia: lamtoro; petai belalang
• Marquesas: atiku
• Marshall Islands: tangan tangan; tangan-tangan
• Mexico: calguaje; dormilon; efe; guache; guache tierra caliente; guaje; guaje blanco; guaje verde; guas; guash; guash de castilla; guashe; guaslim; guaxin; huaxe; huaxim; huaxin; liliak; tumbapelo; uaxi; uaxim; uaxin; waxim; xaxim
• Micronesia, Federated states of: tangantangan
• Nauru: bin
• Niue: pepe; tavahi kaku
• Palau: telengtungd; telentund
• Papua New Guinea: kunai
• Peru: arabisca
• Philippines: elena; giant ipil-ipil; ipil-ipil; kariskis; palo marina
• Puerto Rico: Acacia palida; hediondilla; tantan; zarcilla
• Samoa: fua pepe; fuapepe; lopa Samoa; lusina
• South Africa: reuse wattle
• Thailand: kra thin; to-bao
• Tonga: siale mohemohe
• USA: lead tree; white lead tree
• Vietnam: bo chet; keo dau; schemu

EPPO code

• LUAGL (Leucaena leucocephala)

Summary of Invasiveness

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Fabales
•                         Family: Fabaceae
•                             Subfamily: Mimosoideae
•                                 Genus: Leucaena
•                                     Species: Leucaena leucocephala

Description

A small tree, commonly reaching 3-15 m tall and 10-35 cm in bole diameter; and older trees may reach 20 m tall and 50 cm in diameter. Form varies from shrubby and highly branched in subsp. leucocephala to arborescent with a short clear bole to 5 m, upright angular branching and an open, rounded crown in subsp. glabrata. Bark is mid grey-brown with shallow rusty orange-brown vertical fissures; slash reddish. Leaves bipinnate with 4-9 pairs of pinnae per leaf and 13-21 pairs of leaflets per pinna. The leaflets are small, 9-21 mm long, 2-4.5 mm wide, linear-oblong or weakly elliptic, acute at the tip, rounded to obtuse at the base and glabrous except on margins, with a concave, cup-shaped, elliptic petiole gland. Flowers arranged on compact globose heads, the flower heads in groups of 2-6 in leaf axils arising on actively growing young shoots, the leaves developing simultaneously with the flowers, the heads 12-21 mm in diameter with 100-180 flowers per head, the flowers white. Hairy anthers (visible with a hand lens) distinguish Leucaena from all other mimosoid legume genera. Pods are 9-19 cm long, 13-21 mm wide, linear-oblong and flat with papery pod walls, mid- to orange-brown, glabrous and slightly lustrous (subsp. glabrata and subsp. ixtahuacana), or densely covered in white velvety hairs (subsp. leucocephala), arranged in clusters of 3-20, and occasionally up to 45, per flower head.

Plant Type

Distribution

There is no doubt that L. leucocephala originates from Mexico. However, its true natural distribution is extremely difficult to ascertain in detail because it is cultivated throughout Mexico and Central America, and no unambiguously natural populations have so far been located. Thus earlier references to it being native to Guatemala and Belize are not included here, nor are the assertion from USDA-NRCS (2007) that it is native to the USA.

Subsp. leucocephala is distributed mainly in the Yucatán Peninsula, in the Mexican States of Tabasco, Campeche, Quintana Roo and Yucatán, extending south into northern Belize. Outlying occurrences include an area of central-north Veracruz, and sporadic occurrences across the Isthmus of Tehuantepec into the State of Oaxaca. Despite the great abundance and widespread occurrence of subsp. leucocephala throughout the Yucatán, it is doubtfully native there (McClay, 1990; Waage, 1990; Hughes, 1998b), possibly introduced in pre-Columbian times for its edible seeds and pods and having since spread following introduction. As an aggressive colonizer of disturbed sites, especially on calcareous soils, its present-day abundance in the Yucatán Peninsula may be as an introduced weed rather than a native species (Hughes, 1998a, b).

The natural distribution of subsp. glabrata is also unclear. Despite intensive field exploration, no unequivocally natural populations have so far been located. Within Mexico and Central America it is extremely common as a cultivated backyard, street and orchard tree and is found in the majority of villages and towns in Mexico, in all tropical and subtropical areas (wet, seasonally dry and semi-arid), except above 2000 m altitude, but is only locally naturalized.

Subsp. ixtahuacana is restricted to a small area of northern Guatemala and the immediate border zone in Mexico. As far as is known, subsp. ixtahuacana has not been introduced elsewhere.

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

History of Introduction and Spread

Herbarium specimens recorded by ILDIS (2007) recorded presence on the Portuguese Atlantic island of Madeira and on the mainland although the exact locations and frequency are not known. L. leucocephala has also been positively recorded in southern Spain from field surveys (Dana et al., 2005), and was noted to be “naturalised or on the way to naturalization”; further information on spread and risk of invasion is provided. Thus, L. leucocephala could pose a risk of invasion in more frost-free areas around the Mediterranean, and other more frost-tolerant species or hybrids would also be likely to have a further increased risk of spread.

Risk of Introduction

In South Africa it is declared a category 2 weed in the Western Cape and a category 2 weed across the rest of the country, according to the Conservation of Agricultural Resources Act, 1983 (Henderson, 2001). Federal Highway Administration (2001) list L. leucocephala and L. leucocephala var. K-8 as invasive species on Puerto Rico, classing var. K-8 as one of the most problematic invasives on the island. Space et al. (2000) list it among a number of species that are invasive elsewhere in the world and cultivated, common or weedy on the pacific island of Chuuk. A risk assessment on L. leucocephala (PIER, 2007) confirmed too little of what had become clear decades before, that it should not be imported into Australia and was likely to be of high risk in the Pacific.

Habitat

L. leucocephala is now naturalized and weedy in many areas (Cronk and Fuller, 1995; Hughes, 1998b). It is a weed of open, often coastal habitats, semi-natural, disturbed, degraded habitats, other ruderal sites (e.g. roadsides, abandoned fields and waste ground), and occasionally agricultural land where it has been planted as a shade tree over cocoa (Hughes, 1998a). In Sri Lanka, it is invading dry-mixed evergreen forests (Bambaradeniya et al., 2001). Weediness can be a problem in many agricultural situations or where it has been planted and used in land rehabilitation, or even in intensive systems such as forest nurseries (Verma et al., 2005).

Habitat List

Biology and Ecology

Genetics

L. leucocephala is a self-compatible tetraploid of probable hybrid origin. Harris et al. (1994a) showed that the most likely maternal parent species is L. pulverulenta but the paternal parent remains uncertain. Lack of natural populations of L. leucocephala, along with increasing realization of the extent and importance of indigenous domestication of Leucaena as a minor food in Mexico, led Hughes and Harris (1995) and Hughes (1998b) to speculate that L. leucocephala might have arisen in cultivation in pre-Columbian times, possibly in Veracruz, Mexico. Isoenzyme studies (Harris et al., 1994b) have revealed only limited genetic diversity within L. leucocephala. Brewbaker and Sun (1996) found that all 'Common' or 'Hawaiian' type subsp. leucocephala material of the Pacific and indeed of the world outside Mexico, are of a single genotype. It is widely acknowledged that the varieties of subsp. glabrata used in cultivation are also derived from an extremely narrow genetic base (Brewbaker, 1980, 1985; Hughes, 1989, 1998b).

High yield has been a major factor prompting the promotion and adoption of L. leucocephala, following the discovery and distribution of the so-called 'Giant' or 'Salvador' arborescent varieties, now assigned to subsp. glabrata (National Research Council Board on Science and Technology for International Development, 1984; Brewbaker, 1987). The 'Giant' varieties have consistently out-yielded the pantropically naturalized shrubby 'Common' or 'Hawaiian' varieties belonging to subsp. leucocephala by 20-100% in leaf production and up to 250% in wood production (e.g. Bray et al., 1988; Brewbaker et al., 1972; Brewbaker, 1980; Gray, 1967).

On the basis of trials in Hawaii (Brewbaker et al., 1972) and Australia (Gray, 1967), one of the then newly tested 'Giant' or 'Salvador' accessions, designated with the name 'K8', was formally released by the University of Hawaii (Brewbaker, 1975). This accession has dominated planting alongside a handful of others (e.g. K28, K67 and K72). The so called 'Peru' type, which is fast-growing with large leaves like the 'Giant' type, but also branchy like the shrubby 'Common' or 'Hawaiian' type was also used in some areas. The first bred line, cv. 'Cunningham', is an artificial hybrid between the 'Salvador' and 'Peru' types. It was developed in Australia specifically for fodder production and combines the vigour of the 'Salvador' type with the greater branchiness of the 'Peru' type. These accessions (K8, K67, Peru, Cunningham) have subsequently been widely promoted and used throughout the tropics for reforestation (Pound and Martínez-Cairo, 1983; National Research Council, 1984), despite concerns over the genetic vulnerability of only a handful of self-fertile lines, several of which originate from cultivated material, in single 'variety' plantations (Brewbaker, 1980, 1985; Hughes, 1989). Considerable efforts have been devoted to identifying and field testing additional accessions of subsp. Glabrata, however, very little variation in yield or resistance to the Leucaena psyllid pest has been detected (Brewbaker et al., 1972; Wheeler et al., 1987). One accession, K636, sometimes referred to as cv. 'Tarramba', shows greater psyllid tolerance and yield than the widely used K8, K28, K67 and K72 varieties. Three organizations, the University of Hawaii (UH), USA; CSIRO, Australia; and, the Oxford Forestry Institute (OFI, now the Department of Plant Sciences, Oxford University), UK, house important Leucaena germplasm collections (Hughes et al., 1995) including large numbers of accessions of L. leucocephala. A Leucaena germplasm catalogue has been compiled, cross-referencing all collections (Bray et al., 1997).

Artificial hybridization has been the main thrust of breeding efforts to overcome the limitations of L. leucocephala and its inherent lack of genetic and useful diversity (Brewbaker and Sorensson, 1990). L. leucocephala has been the most important parent in hybrid programmes. Useful hybrids between L. leucocephala and other tetraploid species such as L. diversifolia (hybrid KX3) and L. pallida (hybrid KX2) have been produced and are now being used (Sorensson, 1995). L. leucocephala has also been crossed with different diploid species such as L. esculenta, L. pulverulenta and L. trichandra to produce a series of impressive seedless triploid hybrids, but wider use of these hybrids is limited by lack of efficient seed production or vegetative propagation techniques (Sorensson, 1995; Hughes, 1998b).

High crossability within Leucaena (Sorensson and Brewbaker, 1994) means that L. leucocephala may also form spontaneous interspecific hybrids when brought into contact with other species of Leucaena in cultivation. Two such hybrids, the L. leucocephala X L. esculenta (L. X mixtec) hybrid, documented and named by Hughes and Harris (1994) and the L. leucocephala X L. diversifolia (L. X spontanea) identified by Hughes and Harris (1995), are relatively common.

Physiology and Phenology

L. leucocephala is self-fertile and produces prodigious quantities of seed from the first year, more or less continuously throughout the year as moisture permits, across a wide range of environments (Gonzalez et al., 1967; Pan, 1988; Hughes, 1998b). Fruits ripen in 10-15 weeks. It is slightly or completely deciduous depending on the length and severity of the dry season. If the plant is damaged by burning, then regeneration is possible from basal shoots (Cronk and Fuller, 1995).

Reproductive Biology

Generalist pollinators may pollinate this species (Hughes, 1998). L. leucocephala is self-fertile and produces seed from the first year, (Gonzalez et al., 1967; Pan, 1988; Hughes, 1998b). There are between 15,000 and 20,000 seeds per kilogram. Fruits ripen in 10-15 weeks. Seeds are dispersed mainly by gravity and though some are moved by insects and rodents this is a relatively minor process (Hughes, 1998a, b). The hard coats of seeds allow a persistent seedbank to develop (Hughes, 1998a, b).

Environmental Requirements

L. leucocephala is essentially a tropical species requiring warm temperatures of 25-30°C for optimum growth, tolerating temperature maxima as high as 48°C (Hocking, 1993), and with poor cold tolerance and significantly reduced growth during cool winter months in subtropical areas (Brewbaker and Sorensson, 1987; Williams, 1987). Therefore, it grows best in areas below about 1500 m altitude and up to 15-25° north or south of the equator, although it can survive over a much wider range to about 2000 m and to 30° north or south of the equator. L. leucocephala sheds its leaves even after light frosts; heavy frosts kill all above-ground growth, although trees often resprout after dieback. Similarly, L. leucocephala grows well only in sub-humid or humid climates (650-3000 mm) with moderate dry seasons of up to 6-7 months, although it can survive in climates with as little as 300-500 mm rainfall. It grows better in areas with a well-defined dry season (Lascano et al., 1995). A modified description of climatic requirements was prepared by CSIRO (see Booth and Jovanovic, 2000).

L. leucocephala grows well only on freely-drained, neutral, or slightly alkaline soils and is well adapted to soils derived from calcareous parent material including coral. It is known to be intolerant of soils with low pH (below pH 5), low phosphorus, low calcium, high salinity, high aluminium saturation or waterlogging and has often failed under such conditions (Brewbaker, 1987; Shelton and Brewbaker, 1994; Blamey and Hutton, 1995).

Associations

L. leucocephala has the ability to form a symbiotic association with Rhizobium root nodule bacteria, which are able to fix atmospheric nitrogen. Effective nodulation has been lacking in certain environments due to lack of suitable strains of Rhizobium in the soil and inoculation may be required (Halliday and Somasegaran, 1983). Rhizobium strain TAL1145, developed by NifTAL (Nitrogen Fixation by Tropical Agricultural Legumes) has been shown to be an elite strain for L. leucocephala (Somasegaran and Martin, 1986). For other plant and animal associations, refer to Hughes (1998b).

Climate

Latitude/Altitude

Air Temperature

Rainfall

Rain Regime

Soil Tolerances

Soil drainage

• free

Soil reaction

• neutral

Soil texture

• heavy
• medium

Notes on Natural Enemies

Herbivores and pathogens of L. leucocephala have been reviewed by Lenne (1991) and Boa and Lenne (1995). The most important pest of commercial plantings is the insect defoliator, Heteropsylla cubana. Two important diseases caused by fungal pathogens, Camptomeris leaf spot and gummosis have been reported, and a set of lesser-known rusts and other diseases of currently minor importance, listed by Boa and Lenne (1995). Finally, seeds of L. leucocephala are predated by a range of seed-feeding bruchids and other beetles.

L. leucocephala is susceptible to the psyllid defoliator H. cubana, being small, jumping, sap-sucking, plant-lice which damage L. leucocephala trees by feeding on developing shoots and young foliage. The psyllid causes limited tree mortality, but there is severe and cyclical defoliation, deformation, stunting and dieback. H. cubana is a classic example of a natural enemy catching up with an exotic crop species after many years of herbivore-free existence, through its accidental movement to a new area (Beardsley, 1986). Ever since the first reports of H. cubana spreading in 1984, considerable research effort has been mobilized to provide options for its control and management in association with commercial plantings (e.g. Withington and Brewbaker, 1987; Napompeth and MacDicken, 1990; Ciesla and Nshubemuki, 1995). General overviews of the psyllid problem were provided by Napompeth (1990), Bray (1994) and Geiger et al. (1995) and of the biology of H. cubana by Beardsley (1986), Waterhouse and Norris (1987), Hodkinson (1989) and Muddiman et al. (1992). The rapid spread of the psyllid westward from Central America in 1985 to almost encircle the globe within a decade is documented in detail by Muddiman et al. (1992) and Bray (1994). Attempts to document and quantify the impact of psyllid damage have been made by Mella et al. (1990) and Oka (1990), and the severity and scale of damage caused by H. cubana is extremely variable. Damage is often severe in the first two years following arrival of the psyllid, but as local, native control agents adapt and adjust, there is evidence that psyllid populations decline and the damage that they cause decreases with time. However, severe damage in Asia has been attributed, at least in part, to the extremely narrow genetic base of the handful of self-pollinated varieties of L. leucocephala that have been used (e.g. Brewbaker, 1985; Bray, 1994; Geiger et al., 1995). The possibility of identifying and using psyllid-resistant genetic material within Leucaena was proposed by Sorensson and Brewbaker (1987), Bray and Sands (1987) and Bray (1994) as one option to deal with the psyllid problem, alongside other measures such as biological control (reviewed by Mitchell, 1987; Nakahara et al., 1987; McClay, 1990; Waage, 1990). It is continuing to spread, with a first record for Chile in 2002 (Olivares and Burckhardt, 2002), and is likely to reach all countries where L. leucocephala is present).

Camptomeris leaf spot is caused by the fungus Camptomeris leucaenae, which causes leaf spotting (black spots or patches on the underside of the leaflets) and chlorosis, loss of leaflets or whole leaves, and some dieback often associated with secondary pathogens (Lenne, 1980). It is a potentially serious disease causing reduced forage yields and quality particularly in areas with rainfall >2000 mm (Lenne, 1980, 1991). Camptomeris is widespread in Latin America and the Caribbean and has also been reported from Taiwan, the Philippines and India (Boa and Lenne, 1995). L. leucocephala is apparently one of the more susceptible species in the genus (Lenne, 1980).

The cause of gummosis remains uncertain, but appears to be a canker caused by a fungus in the genus Fusarium. Gummosis is described as the most serious disease of L. leucocephala in India (Dutt, 1982) and Sri Lanka, and has also been noted in Hawaii (van den Beldt and Hodges, 1980) and Taiwan.

High proportions of seeds of L. leucocephala in Latin America are eaten by five different bruchid beetles including three species of Acanthoscelides and two species of Stator (Hughes and Johnson, 1996). So far only one bruchid, Acanthoscelides macrophthalmus has been accidentally introduced outside Latin America, into Australia (Jones, 1996), but deliberate introduction for biological control of weedy L. leucocephala is being considered in South Africa (Neser, 1994, 1996). Outside Latin America, Leucaena seeds may be heavily predated by other seed beetles. Records include the square-necked grain beetle Cathartus quadricollis reported on L. leucocephala in the Dominican Republic (Pound and Martínez-Cairo, 1983), Araecerus levipennis in Hawaii (Sherman and Tanashiro, 1956), and Araecerus fasciculatus on L. leucocephala in India (Singh et al., 1981) and the Philippines (Braza and Salise, 1988).

Means of Movement and Dispersal

Seeds are dispersed by gravity, assisted by ground living insects (Cronk and Fuller, 1995), though insect and rodent movement of seeds may be a relatively minor form of dispersal in this species (Hughes, 1998a, b). Rain and water are also likely to be important means of longer range dispersal, especially via floodwaters.

Pathway Causes

Pathway Vectors

Impact Summary

Impact

Economic Impact

No precise information on the negative economic impacts due to invasions of L. leucocephala are available. Reduction in land area for activities such as farming when the species becomes weedy on abandoned cultivated land or pasture, and control operations carry an economic cost, but being a nitrogen-fixing species may means that farmers prefer it as a fallow. While highly useful as a fodder plant, it is toxic to livestock if it is used in too great a quantity in the diet.

Environmental Impact

Risk and Impact Factors

Impact mechanisms

• Allelopathic
• Competition - monopolizing resources
• Competition - shading
• Interaction with other invasive species
• Poisoning
• Rapid growth

Impact outcomes

• Ecosystem change/ habitat alteration
• Modification of fire regime
• Modification of nutrient regime
• Modification of successional patterns
• Monoculture formation
• Reduced native biodiversity
• Threat to/ loss of native species

Invasiveness

• Abundant in its native range
• Fast growing
• Has high genetic variability
• Has high reproductive potential
• Has propagules that can remain viable for more than one year
• Highly adaptable to different environments
• Highly mobile locally
• Invasive in its native range
• Is a habitat generalist
• Pioneering in disturbed areas
• Proved invasive outside its native range
• Reproduces asexually
• Tolerant of shade
• Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc

Likelihood of entry/control

• Difficult/costly to control
• Highly likely to be transported internationally deliberately

Uses

The wood properties of L. leucocephala have been thoroughly investigated and documented (Bawagan, 1983; Pound and Martínez-Cairo, 1983; van den Beldt and Brewbaker, 1985). Most authors have emphasized the potential to use L. leucocephala wood for a wide range of products including domestic and industrial fuel (including electricity generation), poles, posts, sawn timber, furniture, parquet flooring, particle board and pulp. However, the potential to use L. leucocephala for sawn timber is limited by its generally small dimensions usually not greater than 30 cm diameter, its branchiness which limits the lengths of clear bole available and means that the wood is often knotty, and its high proportion of juvenile wood. Nevertheless, there is increasing use of small dimension sawn wood in a number of industries such as flooring, which might mean that there is a larger market for L. leucocephala sawn wood in the future. In practice, the wood is primarily used as a low to medium quality fuelwood and charcoal for domestic household or local industrial use (e.g. lime or pottery kilns), and for small dimension poles. Use of short-rotation L. leucocephala for poles is limited by lack of durability and susceptibility to attack by termites and wood borers (Timyan, 1996). It is a popular fuel, often competing with alternative local species in areas where fuelwood is in short supply (National Research Council, 1984), but not with the higher quality fuelwood obtained from species of Acacia or Prosopis. The promised potential for large-scale use of Leucaena in pulp production or dendrothermal energy plantations has not come to fruition. Indeed, despite much discussion about its wood production potential, L. leucocephala has not become an established or widely cultivated plantation species that is able to compete with the species of Pinus, Eucalyptus or Acacia which dominate tropical plantation forestry.

L. leucocephala has been one of the foremost tropical fodder trees, often being described as the 'alfalfa of the tropics' (Bray, 1986; Pound and Martínez-Cairo, 1983; National Research Council, 1984; Brewbaker, 1987; Shelton and Brewbaker, 1994). L. leucocephala is, in most respects, one of the highest quality and most palatable fodder trees of the tropics (Jones, 1979, 1994; Pound and Martínez-Cairo, 1983; Brewbaker, 1987; Shelton and Brewbaker, 1994; Norton et al., 1995). Leaf quality of L. leucocephala compares favourably with alfalfa (Medicago sativa) in feed value except for its higher tannin content (Jones, 1979) and mimosine toxicity to non-ruminants (Bray, 1995). Leaves of L. leucocephala have high nutritive value (high palatability, digestibility, intake and crude protein content), resulting in impressive animal production with 70-100% increases in animal live-weight gains compared with pure grass pastures (Shelton and Brewbaker, 1994; Jones, 1994). In addition, L. leucocephala is very persistent over several decades of cutting or grazing, is very productive, recovers quickly from defoliation, combines well with companion grasses and can be grazed with minimal losses due to trampling or grazing (Jones, 1994). L. leucocephala has also been used for leaf meal which is milled, pelleted and sold internationally for incorporation in commercial poultry and pig feed providing a significant source of rural income in parts of Indonesia, the Philippines and Thailand (Manidool, 1983; Jones et al., 1992, 1997).

The undesirable (toxic) effects of feeding Leucaena fodder are largely attributed to the non-protein amino acid, mimosine which is converted to DHP (3-hydroxy-4-1(H)-pyridone) in the rumen (reviewed by Jones, 1979, 1994). Mimosine toxicity can be avoided by limiting feed intake of L. leucocephala to less than 30% of the diet (Bray, 1986). However, for ruminants, a much more effective and elegant solution is the introduction of the rumen microbe Synergistes jonesii which is capable of detoxifying mimosine and DHP (reviewed by Jones, 1994). This has largely solved the mimosine problem for ruminants. As a result, interest in the quest for low mimosine Leucaena varieties and hybrids has waned. However, mimosine remains a significant problem for non-ruminants, restricting the use of Leucaena, and is the main disadvantage of Leucaena in leaf meal production compared with alfalfa (Bray, 1995). Work to develop low mimosine varieties and hybrids was reviewed by Bray (1984, 1986, 1995), Bray et al. (1988) and Hutton (1985).

Leaves of L. leucocephala have also been widely used as a green manure in cropping systems. The value of Leucaena leaf litter as a fertilizer from trees maintained over crops is recognized by farmers in Central America, Indonesia and the Philippines (Dijkman, 1950). In parts of Indonesia and the Philippines, L. leucocephala has been used for several decades to create contour hedgerows or live-barrier terraces for erosion control, but with widely recognized benefits in terms of soil fertility (Parera, 1983). More recently, L. leucocephala was one of the first species to be successfully adapted to formal alley farming (Kang et al., 1981, 1985). L. leucocephala leaves are fragile and decompose quickly providing a very rapid, short-term influx of nutrients related to a low C:N ratio (Weeraratna, 1982; Hocking, 1993). It was also found by Torres (1983), Kang et al. (1985), Mureithi et al. (1994) and Palm (1995) that maize yields can be maintained in Leucaena alley farming in the absence of fertilizer inputs. However, because leaves of L. leucocephala decompose so rapidly, they have little value as mulch for weed control which is widely recognized as one of the main benefits of alley farming, particularly in the humid tropics.

In Mexico, L. leucocephala is an important food plant (Casas and Caballero, 1996; reviewed by Hughes, 1998b). Subsp. glabrata is widely cultivated in backyards, gardens and small orchards for the production of edible unripe pods and seeds which are consumed and widely marketed throughout the country. Its unripe pods and seeds are preferred over most other species of Leucaena for food use, due to abundant and virtually year-round production of large pods, the large seed size and its 'sweeter' flavour. L. leucocephala and L. esculenta are the most widely cultivated and marketed species of Leucaena within Mexico. Unripe pods and seeds of Leucaena are also used for food in parts of Asia, including Indonesia, Thailand, the Philippines and Vietnam, (National Research Council, 1984; Brewbaker and Hutton, 1979; Manidool, 1983; Pound and Martínez-Cairo, 1983; Brewbaker, 1987; Jones et al., 1992, 1997; Sampet et al., 1995). Food use of Leucaena in Asia has been further adapted to local culinary practices through use of young leafy shoots as vegetables and in soups (Manidool, 1983), young seedling sprouts (roots of 3-day-old seedlings), and preparation of fermented tempe from Leucaena seeds in parts of Java, Indonesia (Jones et al., 1992, 1997).

Uses List

Animal feed, fodder, forage

• Fodder/animal feed
• Forage

Environmental

• Agroforestry
• Amenity
• Boundary, barrier or support
• Erosion control or dune stabilization
• Land reclamation
• Landscape improvement
• Revegetation
• Shade and shelter
• Soil conservation
• Soil improvement
• Windbreak

Fuels

• Charcoal
• Fuelwood
• Miscellaneous fuels

General

• Botanical garden/zoo
• Research model

Genetic importance

• Gene source

Human food and beverage

• Honey/honey flora

Materials

• Fertilizer
• Fibre
• Green manure
• Miscellaneous materials
• Mulches
• Wood/timber

Medicinal, pharmaceutical

• Source of medicine/pharmaceutical

Ornamental

• Potted plant

Wood Products

Prevention and Control

Control

This was first contemplated in Hawaii (Smith, 1985) and South Africa (Neser, 1994), but is made more difficult by the economic importance of L. leucocephala. Proposals to release the seed-eating bruchid Acanthoscelides macrophthalmus in South Africa were pursued (Neser, 1994) and the organism has been released (Henderson, 2001), beginning in 1999 (Sharatt and Olckers, 2012). This seed predator has since itself invaded the Far East through the South Asian tropics and subtropics, presumably along with the introduction of its host (Tuda et al., 2009) and has also been accidentally introduced into Australia. In South Africa, subsequent study of specificity of the bruchid has confirmed that the decision to release it was justified (Shoba and Olckers, 2010), and the beetle has become widely established in KwaZulu-Natal (where releases were mostly made), but also in Gauteng, Mpumalanga and the North West Provinces (Olckers, 2011). Sharatt and Olckers (2012), however, report that the modest levels of seed damage in their study in South Africa appear insufficient to regulate populations of L. leucocephala. Ramanand and Olckers (2013) suggest high egg mortality as one of several factors limiting efficacy of the beetle in South Africa.

Wu et al. (2013) examine the biology of A. macrophthalmus in relation to its potential for use in integrated control of L. leucocephala in Taiwan.

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Contributors

23/09/13 Updated by:

Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA

22/11/2007 Updated by:

Nick Pasiecznik, Consultant, France

Distribution Maps

• = Present, no further details
• = Evidence of pathogen
• = Widespread
• = Last reported
• = Localised
• = Presence unconfirmed
• = Confined and subject to quarantine
• = See regional map for distribution within the country
• = Occasional or few reports

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