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: Blackwood

General Information

Acacia melanoxylon varies considerably in height from an evergreen shrub up to a large tree with a dense, pyramidal crown; it can grow from 6 - 45 metres tall. The straight, cylindrical bole can be up to 25 metres long, though it usually branches from near the ground; it can be up to 150cm in diameter and larger boles are often buttressed[, , ]. 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 produces a good quality, valuable wood, which is considered by some to be the most valuable of all Australian timbers. The tree is harvested from the wild and is also often cultivated in areas ranging from the warm temperate zone to higher elevations in the tropics[]. It is also grown as a pioneer species for restoring woodland and establishing woodland gardens, is an excellent soil stabilizer and is also often grown as an ornamental.
Blackwood has been considered one of the most important invasive plant species in southern parts of South Africa. It does not aggressively invade closed evergreen forest, but outside the forest it is a serious invader of open and disturbed sites. Seed-feeding weevils of the genus Melanterius can be used as biological control and have been imported in South Africa from Australia for this purpose. For many years a policy of eradication was followed because the tree was perceived as a threat to the indigenous forest, but recent investigations support the opinion that it is gradually replaced by native species in indigenous forest[].

Known Hazards

The wood is an important cause of allergic contact dermatitis in Australia. Quinones such as acamelin and hydroxyflavans such as melacacidin are responsible for the sensitizing activity. Occupational asthma caused by blackwood has also been reported in wood workers[].
The seed of many Acacia species, including this one, is edible and highly nutritious, and can be eaten safely as a fairly major part of the diet. Not all species are edible, however, and some can contain moderate levels of toxins[]. Especially when harvesting from the wild, especial care should be taken to ensure correct identification of any plants harvested for food[].
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. Locally naturalized in S.W. Europe[].

Habitat

Wet forests on good soils up to the montane zone[, ]. Usually an under-storey tree in Eucalyptus forests[]. Swamp forest, riverine rain forest and as understorey component of wet eucalypt forest[].

Properties

Weed Potential	Yes
Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Tree
Height	25.00 m
Growth Rate	Fast
Pollinators	Bees
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

A plant of the warm temperate to subtropical zones, able to be cultivated at higher elevations in the tropics. It shows a wide ecological adaptability in its native Australia. The mean annual temperature in its range is 6 - 19°c. Mature trees can tolerate moderate frost with occasional temperatures down to around -10°c, though young trees are more sensitive[]. The mean annual rainfall is within the range 750 - 2,300mm[]. In tropical Africa it is usually planted in comparatively cool and wet upland regions at elevations around 1,500 - 2,500 metres[].
Requires a sunny position, even as a seedling[]. Grows best in deep, moist and fertile soils, but also succeeds on a wide range of sandy loams and alluvial soils and in wet, nearly swampy places[, ]. Succeeds in a hot dry position[]. Succeeds in any good garden soil that is not excessively limey[]. Most members of this genus become chlorotic on limey soils[].
The tree is fast growing. In plantations in Rwanda during the first 12 years of growth, the increase in height was 1.5 - 2.4 metres per year and in diameter 16 - 19mm per year. In Tanzania 20 year-old planted trees were 25 - 32 metres tall, with a bole diameter of almost 50cm at breast height. Plantation trees in South Africa had a mean diameter increase of 1 - 2cm per year until the trees were 22 years old[].
A major problem in plantation establishment is that young trees often have poor apical dominance when grown in full light, resulting in large numbers of branches and trees of poor bole form[].
Trees may commence flowering when just 2 years old. They are usually prolific seed producers[].
Trees respond well to coppicing, being able to produce new shoots even from old wood[].
A long-lived species, with ages of over 200 years reported from Australia[].
This species produces both phyllodes (basically a flattened stem that looks and acts like a leaf) and true leaves[, ].
The roots are very vigorous and extensive - they often produce suckers in the wild[, ] and can damage the foundations of buildings[].
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 flowers have a penetrating scent[].

Medicinal

Antirheumatic[]. A hot infusion made with the roasted bark is used to bathe sore and rheumatic joints[].

Stem bark material of this species has been shown to be active against some tumors[].

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 also planted to act as a windbreak[, ].
A natural pioneer species within its native range, where it can germinate freely after disturbances in the forest such as fire and clear felling[]. It can be used in reforestation schemes[]. In South Africa it is considered useful as a nurse tree for the rehabilitation of disturbed natural forest. It is used for reforestation in Rwanda and Burundi[].

Other Uses

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

The bark is rich in 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 heartwood is golden brown to dark brown or almost black, often with a reddish tinge and dark steaks; it is distinctly demarcated from the 3 - 10cm wide, white to straw-coloured sapwood. The grain is usually straight, sometimes interlocked or wavy, giving a fiddle-back figure; the texture is fine to moderately fine; the surface is highly lustrous. The wood is hard; of medium weight; moderately durable to durable, though it is readily attacked by termites. It has good machining properties; takes a high polish; glues and stains well; steam-bending properties are good; nailing properties are poor: the wood splits easily and pre-boring is recommended. A very good quality wood with an attractive appearance, it is suitable for high-quality furniture, cabinet making and fancy veneer; and is also used for light construction, tool handles, musical instruments, bent work, turnery and fence posts.[, , , , , , , ].
The wood is used for fuel and to make charcoal[].

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[].