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Acacia mearnsii is a fast-growing leguminous tree native to Southeastern Australia and Tasmania. Common names for it include Black Wattle, Acácia-negra (Portuguese), Australian Acacia, Australische Akazie (German), Swartwattel (Afrikaans), Uwatela (Zulu).

It has been widely introduced to North America, South America, Asia, Europe, Pacific and Indian Ocean islands, Africa, and New Zealand, where it is often used as a commercial source of tannin or a source of firewood for local communities, or for reclaiming degraded areas. A range of other products, such as resins, thinners and adhesives, can also be made from bark extracts, and its timber is used for building materials, the charcoal is used for fuel and the pulp and wood chips are used to produce paper. In rural communities in South Africa the trees are important as a source of building material and fuel. In the introduced ranges, it has often become invasive, and is now known as one of the worst invasive species in the world (Global Invasive Species Database 2011). It threatens native habitats by competing with indigenous vegetation, replacing grass communities, reducing native biodiversity and increasing water loss from riparian zones.

A. mearnsii plays an important role in the ecosystem in its native Australia. As a pioneer plant it quickly binds the erosion-prone soil following the bushfires that are common in the Australian wilderness. Like other leguminous plants, it fixes the atmospheric nitrogen in the soil. Other woodland species can rapidly utilize these increased nitrogen levels provided by the nodules of bacteria present in their expansive root systems. Hence they play a critical part in the natural regeneration of Australian bushland after fires.

The pioneering characteristics that make it beneficial in controlling erosion also contribute to its success as an invasive. In addition, it produces large numbers of long-lived seeds (which may be triggered to germinate en masse following bush fires), and develops a large crown that effectively shades out other vegetation.

Acacia mearnsii trees are unarmed, evergreen and grow 6 to 20 meters high. The branchlets are shallowly ridged; all parts finely hairy; growth tips golden-hairy. Leaves are dark olive-green, finely hairy, bipinnate; leaflets short (1.5 to 4 mm) and crowded; raised glands occur at and between the junctions of pinnae pairs. Flowers are pale yellow or cream, globular flower heads in large, fragrant sprays. Fruits are dark brown pods, finely hairy, usually markedly constricted.

The species is named after American naturalist Edgar Alexander Mearns, who collected the type from a cultivated specimen in East Africa.

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