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 pachyacra is a shrub or tree, often bushy with a casuarina-like appearance; it can grow 1 - 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. It has potential for use as an ornamental.

Known Hazards

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 - Western Australia, southwestern Northern Territory, northwestern South Australia

Habitat

Found in sand in spinifex country[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Tree
Height	3.00 m
Pollinators	Insects
Cultivation Status	Wild

Cultivation Details

Acacia pachyacra is a plant of the hot, arid and semi-arid, subtropical to tropical zone of central Australia, where it is found at elevations up to 500 metres. It grows best in areas where annual daytime temperatures are within the range 12 - 30°c, but can tolerate 5 - 38°c[]. When dormant, the plant can survive temperatures down to about -10°c, but young growth is more tender and can be severely damaged at -1°c[]. It prefers a mean annual rainfall in the range 200 - 300mm, but tolerates 150 - 350mm[].
Requires a sunny position in a well-drained soil[]. Prefers a light to medium soil, which can be dry and of low fertility[]. Found in the wild mainly on red-sand soils with a pH around 4.5 - 5.5[]. Prefers a pH in the range 6 - 7, tolerating 5 - 8[].
The species is short-lived and senesces rapidly within 5 years of establishment[].
The plant has a potential for being a showy ornamental for arid inland areas on sandy soils[].
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 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[].
A member of the ‘Acacia murrayana group’ with phyllodes very similar to those of Acacia subrigida . Perhaps Acacia pachyacra would be better regarded as a subspecies of Acacia murrayana from which it is (rather arbitrarily) distinguished by its narrower phyllodes[].

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 up to 8cm long and 7 - 11mm wide, with dull black, oblong to widely ovate-elliptic or orbicular seeds 4.5 - 5.5mm long[].
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 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:

Acacia pachyacra is used extensively in the mine-site rehabilitation industry, as plants tend to be prolific seeders, are quick growers and the seeds have a natural propensity to be distributed widely, probably by ants is a disturbance[].
An opportunist species, it responds particularly well after fire. It often forms dense thickets in alluvial washes above the main channel of flow lines in bajada slopes. In good seasons it flowers prolifically, and attracts a wide varies of coleopteran and other flying insect to its fragrant flowers. The species also has the ability to resprout advantageously from the base of the stem after mechanical disturbance and after a mild fire also resprouts advantageously from rootstock up to several metres removed from the presumed parent plant[].

Other Uses

The wood is used for fuel[].

Propagation

The seeds of this species usually germinate readily and often without the required dominancy breaking cues for germination[].
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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