Acacia holosericea

Acacia holosericea is a shrub native to tropical and inland northern Australia. It is commonly known as soapbush wattle, soapbush, strap wattle, candelabra wattle, silver wattle and silky wattle.

Description

A shrub or small tree. It grows 5 m tall. There are prickles along the stem. The leaves are twice divided and there are 8-18 pairs of pinnae. There are up to 50 pairs of pinnules on each pinnae. The flowers are yellow. They are in large clusters at the ends of branches. The pods are flattened.

Edible Uses

The seeds are the primary edible part and must be cooked before eating. They can be prepared in the same ways as other small legume seeds, ground into a powder and used as a flavoring in desserts, or added as a nutritious supplement to pastries and breads. Traditionally, dry seeds were ground to a coarse flour, mixed with water, and either eaten as a paste or baked into a cake. The seedpods are openly and strongly curved, 50–100mm long and 3.5–4mm wide, containing very dark brown to black oblong seeds 4–4.5mm long. Acacia seeds are highly nutritious, containing 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 the fatty acids, which are largely unsaturated. Energy content is high, at 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 delaying the onset of exhaustion during prolonged exercise.

Traditional Uses

The seeds are eaten. The seeds are ground into flour then cooked as flat bread. The roots of young plants are roasted and eaten. The clear gum can also be eaten.

Medicinal Uses

The bark, as with all Acacia species, contains tannins in varying quantities and is astringent. Taken internally, astringents are used to treat diarrhoea, dysentery, and internal bleeding. Applied externally as a wash, they treat wounds and skin problems, haemorrhoids, perspiring feet, and some eye problems, and can be used as a mouthwash. Many Acacia trees also yield gum from the trunk and stems, which is sometimes taken internally to treat diarrhoea and haemorrhoids.

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.

Distribution

It is a tropical plant. It grows in the Kimberleys in Western Australia and also in Queensland. It is often along the edges of streams. It is a tropical plant but adapts to sub tropical places. It is damaged by drought and frost. It often starts the re-growth when an area is cleared. It needs a sunny position. It grows in areas with annual rainfall between 230-2250 mm. It usually grows below 300 m above sea level. It grows in areas with annual average temperatures between 20°-29°C. It can grow in arid places.

Where It Grows

Asia, Australia*, Burkina Faso, India, Indochina, Kenya, Niger, Nigeria, Pacific, Papua New Guinea, PNG, Sahel, SE Asia, Senegal, Sudan, Vietnam, West Africa,

Cultivation

The seed are highly nutritious having 21% protein, 10% fat and 57% carbohydrate. Plants flower April to July in the southern hemisphere and fruit September to October. 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. Carbon Farming - Cultivation: historic wild staple, new crop. Management: standard, coppice.

Propagation

Seed.

Other Uses

This species is a colonising plant that forms dense regrowth in disturbed sites including roadsides and burnt-over areas, making it useful 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 component 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 it may be used in a wide alley cropping system of about 20 metres between rows, where its benefits as a low windbreak may outweigh its depletion of soil moisture in the crop root zone. A red dye can be obtained from the lipid-rich arils by soaking them in water. The heartwood is dark brown, clearly demarcated from the pale sapwood; the wood is hard and dense, suitable for small decorative articles and light construction. It is also an excellent source of firewood and charcoal, with a calorific value of 4670 kcal/kg for the wood and 7535 kcal/kg for the charcoal.

Production

It is a fast growing plant. Plants flower from June to August and produce pods from July to October. Plants may only last 5-6 years. Seeds are separated from the pods by winnowing in the wind.

Other Information

It is used for food in Australia but it is not known to be eaten in PNG.

Notes

There are about 1,350 Acacia species. Over 1,000 occur in Australia. Parts of this plant are used as medicine. It is a tetraploid plant sometimes confused with A. colei. Also as Mimosaceae.

Nutrition

Synonyms

Also Known As

Keo la-sim, Keo to, Silky wattle, Silver-leaved wattle, Soap Bush, Velvet wattle

References (40)

• Anon., 2003, Native Plants for the Fitzroy basin. Society for Growing Australian Plants Inc. (Rockhampton Branch)
• Beasley, J., 2011, Plants of Tropical North Queensland - the compact guide. Footloose publications. p 50
• Bindon, P., 1996, Useful Bush Plants. Western Australian Museum. p 16.
• Bodkin, F., 1991, Encyclopedia Botanica. Cornstalk publishing, p 20
• Brock, J., 1993, Native Plants of Northern Australia, Reed. p 63

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