Acacia saligna
Encyclopedia
Acacia saligna, commonly known by various names including coojong, golden wreath wattle, orange wattle, blue-leafed wattle, Western Australian golden wattle, and, in Africa
, Port Jackson willow, is a small tree
in the family
Fabaceae
. Native to Australia
, it is widely distributed throughout the south west corner of Western Australia
, extending north as far as the Murchison River
, and east to Israelite Bay
.
Acacia saligna grows as a small, dense, spreading tree with a short trunk and a weeping habit. It grows up to eight metres tall. Like many Acacia
species, it has phyllodes rather than true leaves; these can be up to 25 centimetres long. At the base of each phyllode is a nectary gland
, which secretes a sugary fluid. This attracts ants, which are believed to reduce the numbers of leaf-eating insects. The yellow flowers appear in early spring and late winter, in groups of up to ten bright yellow spherical flower heads. The fruit is a legume, while the seed is oblong and dark to black in colour.
A natural colonizer, Coojong tends to grow wherever soil has been disturbed, such as alongside new roads. Its seeds are distributed by ants, which store them in their nests to eat the seed-stalks. Disturbance of the soil brings them to the surface and allows them to germinate. Seeds germinate readily, and hundreds of seedlings can sometimes be found beneath a single parent tree. It is also extremely vigorous when young, often growing over a metre per year.
, revegetation, animal fodder, mine site rehabilitation, firewood, mulch
, agroforestry and as a decorative plant.
Acacia saligna has been planted extensively in semi-arid areas of Africa, South America and the Middle East as windbreak
s and for stabilisation of sand dunes or erosion.
It was planted in the northern suburbs of Sydney in the 1950s by well-meaning native plant enthusiasts, and has subsequently become a major weed in eastern New South Wales
, Victoria
and South Australia
.
, it proliferated at an uncontrollable rate, having been introduced in the nineteenth century to produce tan bark and to stabilise the sands of the Cape Flats
outside Cape Town
after the indigenous bush had largely been cut down for firewood. In addition to replacing indigenous fynbos
vegetation, it also hampers agriculture. It is listed as an invasive alien plant in the Cape Floristic Region
of South Africa, where it has displaced native species through changing fire regimes. The introduction of the acacia gall rust fungus, (Uromycladium tepperianum), has proven to be highly effective at reining it in, reducing density by 80%. The acacia seed weevil,(Melanterius species) was introduced in 2001 and has now (in 2007) reached the stage where there are sufficient numbers available to begin its distribution. It is hoped that it will reduce the seed production to a level where there is not enough seed available for stands to regenerate at a high density after fires. It is also smoked by Khoi tribes.
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, Port Jackson willow, is a small tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Fabaceae
Fabaceae
The Fabaceae or Leguminosae, commonly known as the legume, pea, or bean family, is a large and economically important family of flowering plants. The group is the third largest land plant family, behind only the Orchidaceae and Asteraceae, with 730 genera and over 19,400 species...
. Native to Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, it is widely distributed throughout the south west corner of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, extending north as far as the Murchison River
Murchison River (Western Australia)
The Murchison River is the second longest river in Western Australia. It flows for about from the southern edge of the Robinson Ranges to the Indian Ocean at Kalbarri. It has a mean annual flow of about 200 million cubic metres.-Course:...
, and east to Israelite Bay
Israelite Bay, Western Australia
Israelite Bay is a bay and locality at Location on the south coast of Western Australia - frequently mentioned in Bureau of Meteorology weather reports as a geographical marker - it does not have a climate record....
.
Description
Acacia
Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...
species, it has phyllodes rather than true leaves; these can be up to 25 centimetres long. At the base of each phyllode is a nectary gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...
, which secretes a sugary fluid. This attracts ants, which are believed to reduce the numbers of leaf-eating insects. The yellow flowers appear in early spring and late winter, in groups of up to ten bright yellow spherical flower heads. The fruit is a legume, while the seed is oblong and dark to black in colour.
A natural colonizer, Coojong tends to grow wherever soil has been disturbed, such as alongside new roads. Its seeds are distributed by ants, which store them in their nests to eat the seed-stalks. Disturbance of the soil brings them to the surface and allows them to germinate. Seeds germinate readily, and hundreds of seedlings can sometimes be found beneath a single parent tree. It is also extremely vigorous when young, often growing over a metre per year.
Uses
Acacia saligna can be used for multiple purposes, as it grows under a wide range of soil conditions into a woody shrub or tree. It has been used for tanningTanning
Tanning is the making of leather from the skins of animals which does not easily decompose. Traditionally, tanning used tannin, an acidic chemical compound from which the tanning process draws its name . Coloring may occur during tanning...
, revegetation, animal fodder, mine site rehabilitation, firewood, mulch
Mulch
In agriculture and gardening, is a protective cover placed over the soil to retain moisture, reduce erosion, provide nutrients, and suppress weed growth and seed germination. Mulching in gardens and landscaping mimics the leaf cover that is found on forest floors....
, agroforestry and as a decorative plant.
Acacia saligna has been planted extensively in semi-arid areas of Africa, South America and the Middle East as windbreak
Windbreak
A windbreak or shelterbelt is a plantation usually made up of one or more rows of trees or shrubs planted in such a manner as to provide shelter from the wind and to protect soil from erosion. They are commonly planted around the edges of fields on farms. If designed properly, windbreaks around a...
s and for stabilisation of sand dunes or erosion.
Invasive potential
Acacia saligna has become an invasive species outside its natural range due to the following contributing factors:- Widespread planting outside its native area
- Rapid growth in soil with low levels of nutrients
- Early reproductive maturity
- Large quantity of seeds produced
- Ability of seeds to survive fire
- Ability to germinate after cutting or burning
- Tolerance to many different substratesStratumIn geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
- Nitrogen fixationNitrogen fixationNitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...
- Extensive root system
- Taller growth (by more than 3m in some places) than indigenous plants
It was planted in the northern suburbs of Sydney in the 1950s by well-meaning native plant enthusiasts, and has subsequently become a major weed in eastern New South Wales
New South Wales
New South Wales is a state of :Australia, located in the east of the country. It is bordered by Queensland, Victoria and South Australia to the north, south and west respectively. To the east, the state is bordered by the Tasman Sea, which forms part of the Pacific Ocean. New South Wales...
, Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
and South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
.
Environmental impact in South Africa
In South AfricaSouth Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, it proliferated at an uncontrollable rate, having been introduced in the nineteenth century to produce tan bark and to stabilise the sands of the Cape Flats
Cape Flats
The Cape Flats is an expansive, low-lying, flat area situated to the southeast of the central business district of Cape Town. To many people in Cape Town, the area is known simply as 'The Flats'....
outside Cape Town
Cape Town
Cape Town is the second-most populous city in South Africa, and the provincial capital and primate city of the Western Cape. As the seat of the National Parliament, it is also the legislative capital of the country. It forms part of the City of Cape Town metropolitan municipality...
after the indigenous bush had largely been cut down for firewood. In addition to replacing indigenous fynbos
Fynbos
Fynbos is the natural shrubland or heathland vegetation occurring in a small belt of the Western Cape of South Africa, mainly in winter rainfall coastal and mountainous areas with a Mediterranean climate...
vegetation, it also hampers agriculture. It is listed as an invasive alien plant in the Cape Floristic Region
Western Cape
The Western Cape is a province in the south west of South Africa. The capital is Cape Town. Prior to 1994, the region that now forms the Western Cape was part of the much larger Cape Province...
of South Africa, where it has displaced native species through changing fire regimes. The introduction of the acacia gall rust fungus, (Uromycladium tepperianum), has proven to be highly effective at reining it in, reducing density by 80%. The acacia seed weevil,(Melanterius species) was introduced in 2001 and has now (in 2007) reached the stage where there are sufficient numbers available to begin its distribution. It is hoped that it will reduce the seed production to a level where there is not enough seed available for stands to regenerate at a high density after fires. It is also smoked by Khoi tribes.
External links
- Purdue University Center for New Crops and Plants Products s.v. Acacia saligna.
- 'Beating the Australian: The Acacia Gall Rust Fungus is Winning the Battle against Port Jackson' Veld & Flora Vol 93(2) June 2007 p104 et seq
- 'Invasive Plants are Harming our Biodiversity' Veld & Flora Vol 93(2) June 2007 p108 et seq
- Australian agricultural department fact sheet: http://nt.ars-grin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Uromycladiumtepperianum