Classification of the genus Acacia (in the wider sense) has been subject to considerable debate. It is generally agreed that there are valid reasons for breaking it up into several distinct genera, but there has been disagreement over the way this should be done. As of 2017, it is widely (but not completely) accepted that the section that includes the majority of the Australian species (including this one) should retain the name Acacia, whilst other sections of the genus should be transferred to the genera Acaciella, Mariosousa, Senegalia and Vachellia[].
This species is closely related to Acacia dealbata[]. Hybrids between Acacia baileyana and Acacia decurrens are common[].

Common Name: Green Wattle

General Information

Acacia decurrens is an evergreen shrub or small tree, usually growing no more than 5 - 15 metres tall, though larger specimens up to 22 metres are known. Able to spread by means of suckers, the plant can form dense thickets[, ].
The plant is harvested from the wild for local use as a food, medicine and source of materials. It is commonly cultivated for the tannins in its bark; its wood, fue and charcoal; and also for pulp. It is sometimes grown as a shade tree, and is also used for wind protection and as an ornamental, where it is valued especially for its floral display, in regions from the warm temperate to the tropical zone[].
Often cultivated as an ornamental and for its many uses, in favourable conditions Acacia decurrens has become an invasive weed, spreading by means of seeds and suckers. It is listed as invasive in several countries, including New Zealand, Ethiopia, Zimbabwe and Hawaii[].

Known Hazards

Especially in times of drought, many Acacia species can concentrate high levels of the toxin Hydrogen cyanide in their foliage, making them dangerous for herbivores to eat.

Botanical References

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Range

Australia - New South Wales, Tasmania, Victoria.

Habitat

Sheltered forests, mainly on shales and sandstone[]. Usually on cool moist hills and gullies[]. Grows in open forest or woodland, on hillsides or gullies, usually on shale[].

Properties

Weed Potential	Yes
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	12.00 m
Growth Rate	Fast
Pollinators	Insects
Self-fertile	Yes
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Acacia decurrens is a plant of the warm temperate and subtropical zones, where it is found at elevations up to 2,500 metres; and is also cultivated in the tropics, often above 1,000 metres[, ]. It grows best in areas where annual daytime temperatures are within the range 12 - 25°c, but can tolerate 6 - 30°c[]. When dormant, the plant can survive temperatures down to about -5°c, but young growth can be severely damaged at 0°c[]. It prefers a mean annual rainfall in the range 900 - 2,600mm, but tolerates 750 - 3,000mm[]. This species is one of the hardiest members of the genus, it succeeds outdoors in areas where frosts are mild and only experienced occasionally - in areas close to its climatic limits it tends to do best when grown in coastal gardens in a sunny, sheltered position that is protected from the wind[]. It can resprout from the base if cut bck by frost[]. It requires hot, sunny summers if it is to ripen its wood fully and flower freely.
Prefers a freely-draining, light sandy loam and a very sunny position sheltered from strong winds[, , , ]. Plants can succeed in the poorest of soils, even pure sands[]. Prefers a pH in the range 5 - 6.5, tolerating 4.5 - 7[]. Succeeds in any good garden soil that is not excessively limey[], it also succeeds in dry soils. Most species in this genus become chlorotic on limey soils[]. Established plants are very drought tolerant[].
A fast-growing and very ornamental tree[, ]. It tends to be short-lived, often starting to decline in vigour after 10 - 15 years[].
Trees can be coppiced[].
Seedlings usually germinate in abundance following a forest fire, and can reach a height of 3 - 4 metres after two years[].
The cultivar 'Mollis' is notably resistant to honey fungus[].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[].

Edible Uses

Flowers - cooked[]. Rich in pollen, they are often used in fritters.

A gum that exudes naturally from the trunk is edible and is used as a substitute for Gum Arabic in making jellies etc[, , ]. It is insoluble in water[] and is of low quality[]. Larger quantities can be obtained by tapping the trunk[]. Some plants produce a gum that is dark and is liable to be astringent and distasteful, but others produce a light gum and this is sweet and pleasant. It can be sucked like candy or soaked in water to make a jelly.[]. The gum can be warmed when it becomes soft and chewable[].

Medicinal

The bark is astringent[, ]. It should be stored for 12 months before being used[]. Its main use is in the treatment of diarrhoea and dysentery[, ].

Many Acacia trees yield more or less of a gum from the trunk and stems. This is sometimes taken internally in the treatment of diarrhoea and haemorrhoids[].

Agroforestry Uses:

The extensive root system of this plant helps to prevent soil erosion[].
Often grown as a screen in Australia[], the tree has been widely planted in various countries in order to provide wind shelter, shade for crops, soil fertilization[].
The flowers produce medium to abundant quantities of pollen during good flowering seasons and are a potential source of bee forage[].

Other Uses

The tree yields a copious quantity of gum during the summer months[, ]. In colour, it is amber of all shades, but often it is one of the darkest of wattle-gums.[] It is scarcely soluble in water, but swells up in that liquid to a great extent. After several days boiling in a large quantity of water it almost entirely dissolves. When quite dry it feels horny under the teeth, though with smart blows it may be reduced to powder[]. It can be used as a substitute for gum arabic (see Vachellia nilotica) and to make jelly-like confection[].

The seeds yield a pale-brown fatty oil[]. They have a high oil content with potential for use as a 'drying oil'[].

Dyes extracted from the leaves have been used to colour wool yellow or green depending on the mordant used[].
A yellow dye is obtained from the flowers[].
A green dye is obtained from the seed pods[].

The bark contains about 40% tannin[, ]. On a 10% moisture basis, the bark contains 36.6% tannin[]. Bark harvested for its tannins should only be taken from mature stems, and only when the sap is rising at the beginning of the growing season - which is when the tannin content is highest and the bark is most easily removed from the wood[].

The wood is light in weight, tough and strong[]. Of good quality, it has been used for building poles, mine props, fence posts and hardboard production. In produces a high quality pulp that has low bulk, high bursting strength and high breaking length. It is readily bleached to high brightness levels and is suitable for end products such as fine writing and printing papers[].
The wood is commonly used for fuel and to make charcoal[]. It provides an excellent fuel, burning well even when green[, ].

Propagation

Seed - best sown as soon as it is ripe in a sunny position in a warm greenhouse[].The dried seed of most, if not all, members of this genus has a hard seedcoat and may benefit from scarification before sowing to speed up germination. This can usually be done by pouring a small amount of nearly boiling water on the seeds (being careful not to cook them!) and then soaking them for 12 - 24 hours in warm water. By this time they should have imbibed moisture and swollen - if they have not, then carefully make a nick in the seedcoat (being careful not to damage the embryo) and soak for a further 12 hours before sowing. Sow the seed in Spring in a greenhouse. As soon as the seedlings are large enough to handle, prick them out into individual pots and grow them on in a sunny position in the greenhouse for their first winter. Plant them out in late spring or early summer, after the last expected frosts, and consider giving them some protection from the cold for their first winter outdoors.
Acacia seeds that have matured fully on the bush and have been properly dried have a hard seed coat and can be stored in closed containers without deterioration for 5 - 10 years or more in dry conditions at ambient temperatures. It is best to remove the aril, which attracts weevils and can lead to moulds forming. The arils are easilyremoved by placing the seeds in water and rubbing them between the hands, then drying the seeds and winnowing them[].
Cuttings of half-ripe wood with a heel, mid summer in individual pots in a frame[]. Overwinter in a greenhouse for the first winter and plant out in their permanent positions in late spring or early summer. Fair percentage[].