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      Leucaena leucocephala seeds (Photo: Dan Clark, USDI National Park Service, Bugwood.org - Click for full size   Leucaena leucocephala stand (Photo: William M. Ciesla, Forest Health Management International, Bugwood.org) - Click for full size   Whole plants of Leucaena leucocephala at Darwin, Northern Territory, Australia (Photo: Colin Wilson) - Click for full size   Leaves, flowers and seed pods of Leucaena leucocephala at Darwin, Northern Territory, Australia (Photo: Colin Wilson) - Click for full size   Leaves, flower and buds of Leucaena leucocephala at Kupang in west Timor, Indonesia (Photo: Colin Wilson) - Click for full size
    Taxonomic name: Leucaena leucocephala (Lam.) De wit
    Synonyms: Acacia leucocephala (Lamark) Link 1822, Leucaena glabrata Rose 1897, Leucaena glauca (L.) Benth. 1842, Mimosa leucocephala Lamark 1783
    Common names: acacia palida (Puerto Rico), aroma blanca (Cuba), balori (Fijian), bo chet (Vietnam), cassis (Vanuatu), false koa (Hawai'i), faux mimosa (French), faux-acacia (French), fua pepe (Samoan), ganitnityuwan tangantan (Yapese), graines de lin (French), guaje (Spanish), guaslim (Campeche-Mexico), guaxin (Maya-Yucatan), horse/wild tamarind (English), huaxin (Spanish), ipil-ipil (Philippines), jumbie bean (English), kan thin (Laos), kanthum thect (Cambodia), koa-haole (Hawai'i), kra thin (Thailand), kratin (Cambodia), lamtoro (Indonesia), lead tree (English), leucaena (English), leucaena, liliak (Totonaco-Veracruz, Mexico), lino criollo (Dominican Republic), lopa samoa (American Samoa), lusina (Samoan), nito (Cook Islands), pepe (Niuean), rohbohtin (Kosrae), schemu (Vietnam), siale mohemohe (Tongan), subabul (India), tamarindo silvestre (Spanish), tangantangan (Chamorro-CNMI), tangan-tangan (Chamorro-Guam), te kaitetua (I Kiribati), telentund (Palauan), tuhngantuhngan (Kosrae), uaxim (Spanish), vaivai (Fijian), vaivai dina (Fijian), vaivai ni vavalangi (Fijian), wild mimosa (Bermuda), wild tamarind (Puerto Rico), zarcilla (Puerto Rico)
    Organism type: tree
    The fast-growing, nitrogen-fixing tree/shrub Leucaena leucocephala, is cultivated as a fodder plant, for green manure, as a windbreak, for reforestation, as a biofuel crop etc. Leucaena has been widely introduced due to its beneficial qualities; it has become an aggressive invader in disturbed areas in many tropical and sub-tropical locations and is listed as one of the ‘100 of the World’s Worst Invasive Alien Species’. This thornless tree can form dense monospecific thickets and is difficult to eradicate once established. It renders extensive areas unusable and inaccessible and threatens native plants.
    Description
    The genus Leucaena is distinguished from all other Mimosoid legumes by its hairy anthers which are easily visible with a hand lens. Leucaena leucocephala is distinguished from other species of Leucaena by its intermediate leaflets and large pods in clusters of 5-20 per flower head. It forms a small to medium-sized thornless tree 3-15 (-20)m tall and 5-50cm bole diameter. The leaves are bipinnate with an elliptic convex extrafloral nectary on the petiole, 4-9 pairs of pinnae and 13-21 pairs of leaflets per pinna. The leaflets are 9-16mm long and 2-4.5mm wide, nearly sessile and strongly asymmetric linear oblong and acute at the apex. The flowers occur in 12-21mm diameter heads, are cream-white, with ten free stamens per flower and hairy anthers. The pods occur in crowded clusters of 5-20 per flower head and are 11-19cm long and 15-21mm wide pendulous, flattened and papery, and passively dehiscent with 8-18 seeds per pod. Three subspecies are recognised, two of which - subsp. leucocephala and subsp. glabrata have been introduced pantropically. These two subspecies correspond to shrubby = subsp. leucocephala variants, sometimes referred to as the Common or Hawai‘ian type, and to the more arborescent = subsp. glabrata variants, sometimes referred to as the Giant or Salvador type.
    Occurs in:
    agricultural areas, coastland, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas
    Habitat description
    Leucaena leucocephala is a weed of open (often coastal or riverine) habitats, semi-natural, disturbed, degraded habitats and other ruderal sites. It was assigned to the category of 'a serious or widespread weed invading semi-natural or natural habitats which are of some conservation interest' by Cronk and Fuller (1995) and as a Category II weed (a species which has a local distribution but either expanding populations, or known potential to invade and disrupt native vegetation elsewhere) in Florida by Gordon and Thomas (1997). It is not known to invade undisturbed closed forest habitats. It tolerates a wide range of rainfall from 500 - 3500mm and withstands strongly seasonal (6-8 month dry season) climates. However, it is not frost hardy and grows poorly, setting less seed in cooler tropical highland sites. The species also grows poorly on the acid soils with high Aluminium saturation that prevail in many humid tropical areas. In broad terms, it thus adapts well to a wide range of tropical and subtropical environments, especially seasonally dry tropical areas.
    General impacts
    Leucaena leucocephala is spreading naturally and has been reported as a weed in more then 20 countries across all continents except Europe and Antarctica. It is a weed of open, often coastal or riverine habitats, semi-natural, and other disturbed or ruderal sites and occasionally in agricultural land. It can form dense monospecific thickets which are reported to be replacing native forest in some areas and threatening endemic species of conservation concern in some areas. Dense thickets, even if not of immediate conservation concern can render extensive areas of disturbed ground unusuable and inaccessible.
    Geographical range
    Native range: Native to Mexico and Central America, although the precise native range is blurred by indigenous cultivation as a minor food plant.
    Known introduced range: Subspecies leucocephala was introduced to the Philippines by the Spanish before 1815 and is now pantropically naturalised. Subspecies glabrata was widely introduced across the tropics in the 1970s and 1980s and is now very widely cultivated throughout the tropics and subtropics.
    Introduction pathways to new locations
    Acclimatisation societies:
    Agriculture:
    Internet sales/postal services:
    Landscape/fauna "improvement":
    Nursery trade: Widely promoted by national and international agricultrual and forestry development agencies for agroforestry and agricultural use.
    People sharing resources: Leucaena is extremely easily moved from farmer to farmer and community to community by seed.
    Taken to botanical garden/zoo:


    Local dispersal methods
    Acclimatisation societies (local):
    Management information
    Preventative measures: In Queensland, Australia, management practices aimed at minimising the risk of spread and invasion are being promoted under a code of good practice for livestock farmers who cultivate Leucaena. The policy endorsed in November 2004 "addresses the need for land use management recommendations over the location, design and management of plantings of the shrub legume leucaena to reduce the weed risk. The policy has been developed by Government agencies with responsibilities for natural resource management following consultation with industry, local governments and community groups" (NRM, 2005).

    A Risk Assessment of Leucaena leucocephala for Hawai‘i and other Pacific islands was prepared by Dr. Curtis Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service. The alien plant screening system is derived from Pheloung et al. (1999) with minor modifications for use in Pacific islands (Daehler et al. 2004). The result is a score of 15 and a recommendation of: "Likely to cause significant ecological or economic harm in Hawai‘i and on other Pacific Islands as determined by a high WRA score, which is based on published sources describing species biology and behaviour in Hawai‘i and/or other parts of the world."

    A Risk assessment of Leucaena leucocephala for Australia was prepared by Pacific Island Ecosystems at Risk (PIER) using the Australian risk assessment system (Pheloung, 1995). The result is a score of 11 and a recommendation of: reject the plant for import (Australia) or species likely to be of high risk (Pacific).

    Biological: A bruchid beetle seed predator, Acanthoscelides macrophthalmus has been deliberately introduced and released in South Africa as a biocontrol agent and the same insect has been accidentally introduced to Australia. The accidental spread of the psyllid insect defoliator Heteropsylla cubana in the mid 1980s can cause cyclical defoliation, but does not kill trees and the psyllid appears to have been brought under control by a number of generalist local (and in some cases introduced) psyllid predators and parasites.

    Integrated management: Once established, Leucaena is difficult to eradicate. It resprouts vigorously after cutting. Cut stumps need to be treated with diesel or other chemicals. Furthermore, the soil seed bank can remain viable for at least 10-20 years after seed dispersal.

    Reproduction
    Self-fertile (promoting seed production even on isolated individuals), some outcrossing, pollinated by a wide range of generalist insects including large and small bees. Resprouts after cutting.
    Flowering and seeding continually thoughout the year as long as moisture permits combined with self-fertility promotes abundant pod and seed set.
    Lifecycle stages
    Trees are generally short-lived (20-40 years). The hard seed coat means that germination occurs over a prolonged period after seed dispersal and that seed can remain viable for long periods (at least 20 years) in the soil.
    This species has been nominated as among 100 of the "World's Worst" invaders
    Reviewed by: Dr. Colin Hughes, Department of Plant Sciences, University of Oxford, OXFORD, UK.
    Compiled by: Under revision
    Last Modified: Monday, 16 August 2010


ISSG Landcare Research NBII IUCN University of Auckland