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 colei is usually a spreading shrub growing 2 - 4 metres tall and wide, occasionally becoming a single-stemmed tree up to 9 metres tall on more fertile sites[, ]. 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 and source of materials - it was a moderately important food source for native Australians. Acacia colei (often under the name Acacia holosericea) is planted in Western Africa on an increasing scale for windbreaks, land rehabilitation and fuelwood production. Its seeds are highly nutritious and have vast potential as a new food crop for dry, sub-Saharan Africa[].

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, Northern Territory, Queensland

Habitat

Acacia-dominated scrubs and tall open shrubland, often developing dense, nearly monotypic populations along dry, stony or sandy drainage lines in disturbed sites such as road verges, gravel pits and burnt areas, growing in a variety of soil types[]

Properties

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

Cultivation Details

Acacia colei is a component of many semi-arid, subtropical to tropical plant communities in northern Australia, where it is found at elevations up to 450 metres[, ]. The mean annual temperature is around 25 - 27°c, rising to around 34 - 40°c in the hot season and falling to 8 - 16°c in the cool season. Light frosts happen occasionally in the most elevated locations. Rainfall is highly erratic, usually ranging from 230 - 725mm[].
Requires a sunny position. The plant is well-adapted to grow on infertile sandy soils that are not adapted to conventional food crops, and can also grow in claypans[]. Prefers a circumneutral soil, but can tolerate a pH ranging from 5.5 - 8.5[]. Established plants are drought tolerant.
Acacia colei is a fast-growing but short-lived species, with a life-span of only 3 - 10 years[].
The plant can produce very heavy seed crops less than two years after planting and might have potential as a new human food in West Africa[]. They have been tested for toxicity and human trials have indicated that, at levels up to 25% of the diet, no anti-nutritional factors have been observed[].
Acacia colei has been used as an ornamental in west Africa, Thailand and northern Australia where its silvery foliage, mass flowering and wide adaptability to different soil types are highly valued[].
The seeds of most acacia species can be quickly and efficiently harvested at full maturity without the need for any specialised equipment, e.g. when a crop is heavy one person can harvest 3-5 kilos of clean seed of Acacia colei or Acacia tumida per hour. Small seed-bearing branches can be cut and beaten on sheets, or bushes can be beaten or shaken directly onto large sheets[].
In Niger, farmers prefer the curly-podded form (var. ileocarpa) because less seed is lost through shattering prior to harvest. In Australia the curved-podded form is preferred by seed collectors because the seed is more easily and completely dislodged from the pod during beating[].
Yields of 4 - 6 kilos of seed have been obtained from the plant[].
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[]. Traditionally, the dry seed was ground to a coarse flour, mixed with water and either eaten as a paste or baked to form a 'cake'[]. The seedpods are openly and strongly curved, 50 - 100mm long and 3.5 - 4mm wide, with very dark, brown to black, oblong seeds 4 - 4.5mm 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 colei is a colonising species, forming dense regrowth populations in disturbed sites, including roadsides and burnt-over areas[]. The plant can be used as a pioneer for restoring native woodland or establishing woodland gardens[].
It has been planted as a windbreak around fields and along roadsides. Its bushy habit to ground level and heavy fall of large slowly decomposing phyllodes enhance its value for sand stabilisation[]. It has given very satisfactory results when planted as the lower part of windbreaks with Eucalyptus camaldulensis[].
The plant has a shallow, wide-spreading root system that competes heavily with nearby crops and can reduce their yields[]. On sandy soils in semi-arid zones, the plant may be used in a wide alley cropping system (about 20 metres between rows) where its benefits as a low windbreak may outweigh its depletion of soil moisture in the crop root zone[].

Other Uses

A red dye can be obtained from the lipid-rich arils by soaking them in water[].

The heartwood is dark brown; it is clearly demarcated from the pale sapwood. The wood is hard, dense. It is suitable for the manufacture of small decorative articles, and can be used for light construction[, ].
The wood is an excellent source of firewood and charcoal. The calorific value of the wood is 4670 kcal/kg and that of the charcoal 7535 kcal/k[].

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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