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[].

Common Name: Golden Wattle

General Information

Acacia pycnantha is an evergreen shrub or small to medium-sized tree that can grow from 5 - 8 metres tall[]. Although it produces leaves as a seedling, llike most members of the genus the mature plant does not have true leaves but has leaf-like flattened stems called phyllodes[].
The tree is one of the richest sources of tannins in the world[]. It is often harvested from the wild for its tannin, which is traded, and is also harvested as a local source of food and materials. It is sometimes cultivated for the tannin obtained from its bark[, ], and is also often planted as an ornamental.
The species has become an environmental weed in some places (eg. Western Australia, California and particularly South Africa where it is a serious pest). It has also naturalised in the NSW Tablelands and in Tasmania so care should be exercised in planting it in areas close to bushland[].

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

, ,

Range

Australia - New South Wales, Southern Australia, Victoria

Habitat

Thickets, or as an under-storey in Eucalyptus forests, especially on very poor soils[]. Grows in sand or loam, in Eucalyptus forest or woodland, open scrub and heath[].

Properties

Weed Potential	Yes
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	6.00 m
Growth Rate	Fast
Pollinators	Insects
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

A plant of the warm temperate zone, where it is found at elevations up to 800 metres. It grows best in areas where annual daytime temperatures are within the range 20 - 28°c, but can tolerate 5 - 35°c[]. When dormant, the plant can survive temperatures down to about -2°c, but young growth can be severely damaged at -1°c[]. It requires hot, sunny summers if it is to ripen its wood fully and flower freely[]. It prefers a mean annual rainfall in the range 1,000 - 1,600mm, but tolerates 600 - 2,300mm[].
Prefers a well-drained, rather poor sandy loam and a very sunny position[, ]. Succeeds in any good garden soil that is not excessively limey and also in dry soils[]. Prefers a pH in the range 6 - 7, tolerating 5 - 7.5[]. Most members of this genus become chlorotic on limey soils[].
A fast growing but short-lived tree in cultivation[]. It can often flower in its second year from seed[].
This tree is the floral emblem of Australia[].
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.

The plant yields an oily gum which is said to be edible[, ]. Some species 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 of all Acacia species contains greater or lesser quantities of tannins and are astringent. Astringents are often used medicinally - taken internally, for example. they are used in the treatment of diarrhoea and dysentery, and can also be helpful in cases of internal bleeding. Applied externally, often as a wash, they are used to treat wounds and other skin problems, haemorrhoids, perspiring feet, some eye problems, as a mouth wash etc[, ].
Many Acacia trees also yield greater or lesser quantities 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[]. It is often planted for this purpose on sandy banks[].

Other Uses

A yellow dye is obtained from the flowers[].
A green dye is obtained from the seed pods[].

An essential oil from the flowers can be used in perfumery[, ].

A gum is obtained from the bark[]. Of low quality[].

The thin bark is rich in tannin[, , ]. On a 10% moisture basis, the bark contains 40.8% 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 close-grained, tough[].

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[].