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:

General Information

Acacia trachycarpa is a shrub or a small tree with resinous branches and a spreading crown that can be flat-topped; it can grow up to 5 metres tall[, ]. Although it produces true leaves as a seedling, like most members of this section of the genus, the mature plant does not have true leaves but has leaf-like flattened stems called phyllodes[].
The plant is harvested from the wild for local use as a food, medicine and source of wood. It has potential as a food crop and is cultivated in arid areas as a fuel crop[, ].

Known Hazards

The phyllodes may contain low levels of cyanogenic glycoside, though they are unlikely to be dangerous to herbivores[].
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

Range

Australia - northwestern Western Australia

Habitat

Found mainly in sandy clay loam derived from alluvium, in a variety of habitats, usually along creeks and rivers, sometime forming thickets on coastal pindan sandplains; at elevations up to 400 metres[, , ].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Shrub
Height	3.00 m
Growth Rate	Fast
Pollinators	Insects
Cultivation Status	Cultivated, Wild

Cultivation Details

Acacia trachycarpa is a plant of the hot arid and semi-arid tropical zone of northwestern Australia, where it is found at elevations up to 400 metres. It grows best in areas where annual daytime temperatures are within the range 22 - 32°c, but can tolerate 8 - 45°c[]. When dormant, the plant can survive temperatures down to about -3°c, but young growth is more tender and can be severely damaged at 0°c[]. It prefers a mean annual rainfall in the range 250 - 350mm, but tolerates 150 - 400mm, experiencing a dry season that can be up to 7 - 8 months[, ].
Requires a sunny position[]. Requires a well drained soil, succeeding in a wide range of textures and tolerant of low fertility[]. Prefers a pH in the range 7 - 8, tolerating 6.5 - 8.5[].
A reasonably fast growing species that is reported to be frost sensitive and not very drought tolerant[].
Plants are killed by intense fires but have the ability to resprout after cool fires or mechanical clearing[]. Coppicing ability is variable, ranging from poor to good[].
The seeds of most acacia species can be quickly and efficiently harvested at full maturity without the need for any specialised equipment. Small seed-bearing branches can be cut and beaten on sheets, or bushes can be beaten or shaken directly onto large sheets[].
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

Seed - cooked[]. It can be eaten in the same ways as other small legume seeds and is also ground into a powder then used as a flavouring in desserts or as a nutritious supplement to pastries and breads[]. The seedpods are 3 - 11cm long and 7 - 12mm wide, with brown to black, oblong to round seeds 5 - 8mm long and 4 - 7mm wide[, ].
Acacia seeds are highly nutritious and contain around 26% protein, 26% available carbohydrate, 32% fibre and 9% fat. The fat content is higher than most legumes with the aril providing the bulk of fatty acids present. These fatty acids are largely unsaturated. The energy content is high in all species tested, averaging 1480 ±270 kJ per 100g. The seeds are low glycaemic index foods - the starch is digested and absorbed very slowly, producing a small, but sustained rise in blood glucose and so delaying the onset of exhaustion in prolonged exercise[].

The ground seed can be used to produce a high quality, caffeine-free coffee-like beverage[].

Medicinal

The boiled young leaves are used to make a sticky liquid for the treatment of skin irritations[].

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 plant can be used for erosion control and stabilizing sand dunes[]. It has also been used as a low windbreak[].

Other Uses

The wood was used traditionally to make spears, fighting sticks and digging tools[].
The wood can be used as fuel and charcoal[, ] The air-dry density of the wood is 770 kg/m3 with a calorific value of 4740 kcal/kg[].

Propagation

The 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.
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[].

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