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Scientific Name
Synonyms
Common Names
Family
Origin
Naturalised Distribution
Cultivation
Habitat
Distinguishing Features
Habit
Seedling
Stems and Leaves
Flowers and Fruit
Reproduction and Dispersal
Impacts
Similar Species
Legislation
Management
Sources
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Click on images to enlarge


a dense colony of this species (Photo: Sheldon Navie)


habit (Photo: Sheldon Navie)


habit in flower (Photo: Sheldon Navie)


young branches and foliage tips covered in a whitish powdery bloom (Photo: Sheldon Navie)


the large twice-compound leaves which are bluish-green or somewhat silvery in colour (Photo: Sheldon Navie)


leaves with numerous pairs of branchlets, each containing many pairs of tiny leaflets (Photo: Greg Jordan)


close-up of a leaf showing the small raised glands, at the junction of each pair of branchlets (Photo: Greg Jordan)


large compound flower clusters (Photo: Trevor James)


numerous small globular flower clusters arranged into elongated compound clusters (Photo: Trevor James)


close-up of the small globular flower clusters and the whitish-coloured flower stalks (Photo: Sheldon Navie)


close-up of seeds with small fleshy arils (Photo: Steve Hurst at USDA PLANTS Database)

Silver wattle
Acacia dealbata subsp. dealbata

Scientific Name

Acacia dealbata Link subsp. dealbata

Synonyms

Acacia dealbata Link
Acacia dealbata Link var. dealbata
Acacia decurrens Willd. forma mollis (Lindl.) Benth.
Acacia decurrens Willd. var. dealbata (Link) F. Muell. ex Maiden
Acacia decurrens Willd. var. mollis Lindl.
Acacia decurrens Willd. var. mollissima E. Miege
Acacia derwentiana A.M. Gray
Acacia puberula Dehnh.
Racosperma dealbatum (Link) Pedley
Racosperma dealbatum (Link) Pedley subsp. dealbatum

Common Names

black wattle, blue wattle, mimosa, silver wattle, Sydney black wattle, Tasmania mimosa

Family

Fabaceae: sub-family Mimosoideae (New South Wales)
Leguminosae (South Australia)
Mimosaceae (Queensland, the ACT, Victoria, Tasmania, Western Australia and the Northern Territory)

Origin

Silver wattle (Acacia dealbata subsp. dealbata) has a relatively widespread natural distribution in south-eastern Australia. It is native to most of eastern New South Wales, the ACT and most of Victoria (in mainland Australia it is most common near the Great Dividing Range from the Ben Lomond Range in northern New South Wales to the Grampians in western Victoria). It is also widespread and common throughout Tasmania.

Note: Another form of this species (i.e. Acacia dealbata subsp. subalpina), which is often smaller in stature with smaller leaves and leaflets, grows mainly at higher altitudes in south-eastern New South Wales, the ACT and north-eastern Victoria (e.g. in the Snowy Mountains). However, Acacia dealbata subsp. subalpina has not become naturalised outside its native range and will not be mentioned any further here.

Naturalised Distribution

Naturalised in south-western Western Australia, south-eastern South Australia and on Norfolk Island. In Western Australia it is naturalised in the the coastal and sub-coastal districts between Perth and Albany. In South Australia it is particularly common near Adelaide and is also present in the extreme south-east of the state.

This species has also become naturalised overseas in southern Africa, New Zealand, southern India, southern Europe, and south-western USA (i.e. California).

Cultivation

Silver Wattle (Acacia dealbata subsp. dealbata) is cultivated in many parts of Australia, as well as overseas, and can often be seen growing as an ornamental in inhabited areas.

Several cultivars have been developed that differ form the description given here, the most common in Australia being a prostrate ground-covering form called Acacia dealbata 'Kambah Karpet'. There is also a variety with weeping stems (which is sometimes called Acacia dealbata var. pendula) and numerous other varieties that were developed in southern France, but these are mostly grown overseas.

Habitat

Grows naturally in open woodlands, dry sclerophyll forests and wet forests at altitudes usually ranging from 350-1000 metres in many parts of south-eastern Australia. Within these areas in grows in deep gullies, on slopes, on high plateaus, on creekbanks and near swamp margins.

Silver wattle (Acacia dealbata subsp. dealbata) has become naturalised on stony slopes, along creekbanks and on roadsides in South Australia and Western Australia.

In New Zealand it grows in waste places and along dry riverbeds, in South Africa it invades grasslands, roadsides and watercourses, and in California it grows in disturbed sites and along roadsides.

Distinguishing Features

Habit

A large bushy shrub or spreading tree usually growing 1.5-10 m tall, but occasionally reaching up to 30 m in height.

Seedling

The seedlings have two small and narrow undivided seed-leaves (i.e. cotyledons). The first true-leaf is usually once-compound, with a few pairs of leaflets (i.e. pinnate), while the second true-leaf is usually twice-compound (i.e. bipinnate), with a single pair of branchlets (i.e. pinnae).

Stems and Leaves

The bark of this species is mostly smooth and either grey, greyish-brown, brown or dark brown in colour. However, older trunks may become deeply fissured. Younger branches are rounded or slightly angular with ridges towards their tips. These branches are usually finely hairy and conspicuously bluish-green (i.e. glaucous) or whitish in colour due to the presence of a powdery substance (i.e. they are pruinose). The young foliage-tips are white, whitish-yellow or cream-coloured and densely covered in fine hairs (i.e velvety-tomentose).

The leaves are twice-compound (i.e. bipinnate) and usually somewhat bluish-grey or silvery-green in colour (i.e. they are slightly to very glaucous). These leaves (6-17 cm long) are alternately arranged along the stems and have a short hairy leaf stalk (i.e. petiole) that is 1 to 15 mm long. The extension of this stalk (i.e. rachis), which bears numerous (10-30) pairs of leaf branchlets (i.e. pinnae), is 3-17 cm long (usually 5-10 cm long). It is finely hairy and bears a small raised structure (i.e. gland) at the junction of the each of the pairs of branchlets (i.e. pinnae). The leaf branchlets (15-55 mm long) each bear numerous (14-68) pairs of small, narrowly oblong to linear leaflets (i.e. pinnules). These leaflets (1.5-6 mm long and 0.4-1 mm wide) are very crowded and have rounded or pointed tips (i.e. obtuse to acute apices). Their upper surfaces are mostly hairless (i.e. glabrous), while their margins and lower surfaces are usually finely hairy (i.e. pubescent).

Flowers and Fruit

The small yellow or golden-yellow flowers are very fluffy in appearance due to the presence of numerous stamens. These flowers have five relatively inconspicuous petals and sepals and are densely arranged into small globular clusters (4-7.5 mm across), each containing 22-42 flowers. The small globular flower clusters are borne on short stalks (i.e. peduncles) 2-6 mm long that are finely hairy and usually whitish-grey in colour. These globular flower clusters are alternately arranged along a small branch emanating from the forks (i.e. axils) of the leaves, or occasionally borne at the tip of the stem. The branches are often somewhat zig-zagged in nature and may or may not be branched (i.e. they form axiallry or terminal racemes or panicles). Flowering generally occurs during late winter and spring (i.e. from July to November).

The fruit is an elongated and somewhat flattened pod (20-115 mm long and 6-14 mm wide). These pods are not, or only slightly, constricted between some or all of the seeds and are either straight or slightly curved. They are bluish-green (i.e. glaucous) or covered in a whitish powdery substance (i.e. pruinose) when young and generally turn greyish-brown or purplish-brown in colour as they mature. Fruit are normally present during late spring and summer (i.e. mostly from November to January, but sometimes through to March). Each pod contains several seeds (about 4 mm long) that have a small fleshy structure (i.e. aril) attached to them.

Reproduction and Dispersal

Reproduction of silver wattle (Acacia dealbata subsp. dealbata) is mainly by its long-lived seeds. However, this species is also known to produce numerous suckers when its roots are damaged.

Seeds may be dispersed short distances by ants that collect them and transport them to their nests. The pods, each containing several seeds, may be spread by wind and water. The seeds may also be dispersed in dumped garden waste and contaminated soil.

Impacts

Silver wattle (Acacia dealbata subsp. dealbata) is widely cultivated in Australia and has become a garden escape beyond its native range in Western Australia and South Australia. Its seeds germinate readily after fire and it can form dense thickets.

In Western Australia it grows in jarrah forest and karri forest at the Porongorups and is also found along roadsides between Perth and Albany. It is considered to be a common environmental weed in the Adelaide region in South Australia, where it is reported to invade native bushland.

Similar Species

Silver wattle (Acacia dealbata subsp. dealbata) may be confused with several other native wattles (Acacia spp.) including black wattle (Acacia mearnsii ), Sydney green wattle (Acacia decurrens ), green wattle (Acacia irrorata), northern silver wattle (Acacia leucoclada), Bodalla silver wattle (Acacia silvestris), dwarf silver wattle (Acacia nanodealbata), Cootamundra wattle (Acacia baileyana ) and Karri wattle (Acacia pentadenia). These species can be distinguished by the following differences:

Hybrids of silver wattle (Acacia dealbata subsp. dealbata) and Cootamundra wattle (Acacia baileyana ) are known to occur, particularly in Vicotria, and they are also considered to be weeds. Such hybrids are intermediate between the two species and can be distinguished from silver wattle (Acacia dealbata subsp. dealbata) by having fewer (i.e. 6-12) pairs of branchlets, with the lowermost pair of branchlets usually being angled slightly backwards (i.e. reflexed).

Note: This page only covers those species that have been reported to be commonly confused with silver wattle (Acacia dealbata subsp. dealbata). For a more in-depth key to all of the wattle (Acacia spp.) present in Australia, see the Wattle: Acacias of Australia CD-ROM or Flora of Australia, Volumes 11A and 11B.

Legislation

Silver wattle (Acacia dealbata subsp. dealbata) is not declared or considered noxious by any state or territory government in Australia.

Management

For information on the management of this species see the following resources:

Sources

Anonymous (2005). Australia's Virtual Herbarium. http://www.anbg.gov.au/avh. Australian National Botanic Gardens, Environment Australia, Canberra, ACT.

Anonymous (2005). Weeds Invading the Bush. Urban Forest - Backyards for Wildlife. http://www.urbanforest.on.net/backyard.htm. SA Urban Forest Biodiversity Program, Blackwood, Adelaide, South Australia.

Anonymous (2006). National List of Naturalised Invasive and Potentially Invasive Garden Plants. Version 1.2. World Wildlife Fund - Australia (WWF Australia).

Barker, B., Barker, R., Jessop, J. and Vonow, H. (2005). Census of South Australian Vascular Plants. Fifth Edition. The Botanic Gardens of Adelaide and State Herbarium, Government of South Australia, Adelaide, South Australia.

Buchanan, A.M. (2007). A Census of the Vascular Plants of Tasmania and Index to The Student s Flora of Tasmania. Web Edition for 2007. http://www.tmag.tas.gov.au/Herbarium/TasVascPlants.pdf. Tasmanian Herbarium, Tasmanian Museum and Art Gallery (TMAG), Hobart, Tasmania.

Green, P.S. (1994). Flora of Australia. Volume 49 - Oceanic Islands 1. Australian Government Publishing Service (AGPS), Canberra, ACT.

Henderson, L. (2001). Alien Weeds and Invasive Plants. Plant Protection Research Institute, Agricultural Research Council, South Africa.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds: a guide to the weeds of Western Australia. The Plant Protection Society of Western Australia, Victoria Park, Perth, Western Australia.

Jordan, G. (2003). Key to Tasmanian Dicotyledons. http://www.utas.edu.au/dicotkey/DicotKey/key.htm. University of Tasmania, Hobart, Tasmania.

Keighery, G. and Longman, V. (2004). The naturalized vascular plants of Western Australia. 1: checklist, environmental weeds and distribution in IBRA regions. Plant Protection Quarterly 19: 12-32.

Kodela, P.G. (2001). Acacia dealbata  Link. Flora of Australia Online. http://www.anbg.gov.au/abrs/online-resources/flora/index.html. Australian Bological Resources Study (ABRS), Commonwealth of Australia, Canberra, ACT.

Kodela. P.G. and Tame, T.M. (2002). Acacia dealbata. New South Wales Flora Online. PlantNET - The Plant Information Network System of Botanic Gardens Trust. http://plantnet.rbgsyd.nsw.gov.au. Royal Botanic Gardens and Domain Trust, Sydney, New South Wales.

Lazarides, M., Cowley, K. and Hohnen, P. (1997). CSIRO Handbook of Australian Weeds. CSIRO Publishing, Collingwood, Melbourne, Victoria.

Maslin, B.R. (2001). WATTLE: Acacias of Australia. CD-ROM. Australian Bological Resources Study (ABRS) and Department of Conservation and Land Management (CALM), Government of Western Australia.

Moore, J. and Wheeler, J. (2002). Southern Weeds and their Control. Department of Agriculture of Western Australia, Perth, Western Australia.

Muyt, A. (2001). Bush Invaders of South-East Australia. R.G. and F.J. Richardson, Meredith, Victoria.

Randall, R.P. (2002). A Global Compendium of Weeds. R.G. and F.J. Richardson, Meredith, Victoria.

Roy, B., Popay, I., Champion, P., James, T. and Rahman, A. (2004). An Illustrated Guide to Common Weeds of New Zealand. Second Edition. New Zealand Plant Protection Society, Lincoln, New Zealand.

Spooner, A. (2002). Acacia dealbata Link. FloraBase: The Western Australian Flora. http://florabase.calm.wa.gov.au. Western Australian Herbarium, Department of Conservation and Land Management (CALM), Perth, Western Australia.

Tame, T., Kodela. P., Conn, B. and Hill, K. (2001). Acacia dealbata. Wattleweb. http://plantnet.rbgsyd.gov.au/WattleWeb/index.php. Royal Botanic Gardens, Sydney, New South Wales.

Walsh, N.G. and Stajsic, V. (2007). A Census of the Vascular Plants of Victoria. Eighth Edition. National Herbarium of Victoria, South Yarra, Victoria.