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Acacia irrorata (Family Fabaceae)

Blueskin, Green Wattle

Distribution:

Acacia irrorata occurs in the coastal belt from south-eastern Queensland to southern New South Wales and extends inland to the tablelands of New South Wales. The subspecies velutinella is common in the coastal areas of New South Wales. The latitudinal range is 25-37o S and it is found from near sea level to 1300 m. (QLD, NSW).

Features:

Acacia irrorata is a fast-growing, large shrub or small tree, usually 5-10 m tall but occasionally up to 20 m. The foliage is dark green, bipinnate, 4-6 cm long with 9-12 pairs of pinnae, each bearing 40-50 pairs of leaflets. The flowers are lemon to pale golden yellow in globular heads. Pods are flat with sparse hairs, slightly constricted between the seeds, 6-10 cm long and 5-10 mm wide. Flowering is from November - February and the seeds are 7-9 months later. There are about 100 000 viable seeds per kilogram and pre-treatment with boiling water for one minute promotes germination.

Ecology/Way of Life:

Green Wattle occurs mainly in the warm, humid zone with some extension into the warm sub-humid and cool, humid zones. Limited areas near the coast are frost-free but elsewhere there may be up to 40 frosts recorded annually. Mean annual rainfall is 750-1100 mm with a weak to moderate summer maximum. It is found on undulating coastal lowlands, mountain slopes and valleys of the coastal escarpment and to a limited extent on the high tablelands. It is common on the heavier soil types derived from shales and basalt. Its best growth is on moist, well-drained, relatively fertile flats along watercourses. This species is a component of tall open-forest, often on rainforest margins, dominated by Eucalyptus saligna, E. microcorys, E. resinifera, E.propinqua or E. pilularis.

Interaction with Humans/Threats:

The heartwood is pale brown, hard and moderately dense. It makes a good fuel and can be used for posts and poles but may not be as durable as many other acacias. The bark is a very good source of tannin. It has a role for shade and tall shelter and also for soil conservation on steep slopes where there is moderately fertile soil. The soft green foliage makes it an attractive ornamental tree. Its ability to regenerate rapidly makes it a potential weed species.

Other Comments:

Acacia irrorata was named by Franz Wilhelm Sieber (1789-1844), a Czechoslovakian who made plant collections in New South Wales in 1923. The name comes from the Greek akakia = a thorny plant, specifically Acacia arabica; and the Latin irrorata = moistened with dew. A subspecies, Acacia irrorata velutinella, takes its name from the Latin velutinus = velvety, referring to the velvety foliage and branchlets which distinguish it from the subspecies irrorata.

Further Reading:

Doran, J.C. and Turnbull, J.W. (eds.) 1997. Australian trees and shrubs; species for land rehabilitation and farm planting in the tropics. ACIAR Monograph no. 24. Australian Centre for International Agricultural Research, Canberra. 384p.

Pedley, L. 1979. A revision of Acacia Mill. in Queensland. Austrobaileya 1: 235-237.

Tame, T. 1992. Acacias of southeast Australia. Kangaroo Press, Kenthurst, Sydney. 206p.

Topics: Plant structure Soils Invasive species/Weeds Vegetation types Timber Ornamental Climatic zones Waterlogging Firewood Germination

Acknowledgments:

Text & map from Australian Trees and Shrubs, courtesy Australian Centre for International Agricultural Research; text edited by J. Turnbull; photo courtesy S. Searle.

Sponsored by:

Suzette Searle/ACIAR


 

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