Leucaena

Other Common Names: Tree Leucaena.

Synonyms: Leucaena glauca, Acacia leucocephala, Acacia glauca, Mimosa leucocephala, Mimosa glauca.

A long-lived shrub or small tree, typically growing 2 to 8 m tall (occasionally up to 20 m) and surviving for more than 40 years. It is self-fertile and produces large quantities of seed from its first year, with pods maturing in 10 to 15 weeks. The hard-coated seeds form a persistent seedbank that can remain viable for over 5 years, although warm and humid conditions can accelerate germination and gradually reduce seed reserves in the soil. It is still promoted as a fodder crop in the Kimberley and Pilbara and has invaded river areas and gorges through wandering cattle.

• Forms a deep root system, with a taproot reaching up to 5 to 6 m deep.

Adapted to tropical and subtropical climates and commonly occurs in coastal areas, open woodlands, gardens, parks, waste areas, disturbed sites and offshore islands. It establishes best in areas with annual rainfall of 650 to 3000 mm, although established plants are highly drought tolerant. Growth is optimal in warm conditions and plants can tolerate temperatures up to 48°C, but frost and prolonged temperatures below 10°C can severely limit growth. It grows on a wide range of soil types, performing best in deep, well-drained, alkaline soils of low to moderate fertility and can tolerate mild salinity. While it tolerates partial shade, the plants prefer full sun and does not persist under a closed forest canopy.

Similar native species: Similar to Indian siris (Albizia lebbeck) but can be distinguished by the Indian siris's much larger leaflets (25 to 40mm long and 10 to 20 mm wide) and powder puff like clusters of pale yellow, cream and greenish white flowers. 

Similar non-native species: Similar to Mimosa bush (Vachellia farnesiana) which has yellow pom-pom like flowers and the foliage is not as dense.

Produces seed year-round and spreads primarily by seed. While seeds are usually dispersed less than 20 m from the parent plant through passive pod shatter, long distance spread occurs primarily via cattle movement. It can also be dispersed via water movement, particularly during flooding events, contaminated hay, soil, mud on vehicles and machinery and occasionally by wind. 

A significant environmental weed due to its ability to produce large quantities of hard-coated seed and establish dense stands. It can outcompete native vegetation, form monocultures that shade out other species and reduce local biodiversity. Dense infestations can also restrict the movement of people and wildlife, while reducing habitat and food for native animals. It poses a particular threat to coastal wetlands and inland riparian zones, where flooding and other disturbance events can facilitate its spread.

Introduced and widely planted as fodder for livestock, particularly cattle. Internationally, it has also been used for timber production, forage and as a green manure.