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 tumida is a multi-stemmed shrub growing 2 - 3 metres tall, or a tree with a well developed canopy growing up to 15 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 and source of materials. Its seeds are highly nutritious and the plant has been recommended as a new food crop for arid tropical regions[]. The plant is also used in soil stabilization projecs, in shelterbelt plantings, and also as an ornamental.

Known Hazards

The seeds have been tested for toxicity and human trials have indicated that, at levels of up to 25% of the total diet, no anti-nutritional factors have been observed[].
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 - northern Western Australia, northwestern Northern Territory

Habitat

Grows in shallow, skeletal, often sandy soils, in rocky gullies, in savannah grassland often with spinifex or on hillsides, on sand plains and coastal sand dunes; at elevations up to 500 metres[, ].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Tree
Height	5.00 m
Growth Rate	Fast
Pollinators	Insects
Cultivation Status	Cultivated, Wild

Cultivation Details

Acacia tumida is a plant of the arid to moist tropical zone of northwest Australia, where it is found at elevations up to 500 metres. It grows best in areas where annual daytime temperatures are within the range 22 - 36°c, but can tolerate 12 - 42°c[]. The plant grows mainly in areas that are frost-free, but can experience very occasional light frosts at higher elevations. It prefers a mean annual rainfall in the range 400 - 1,000mm, but tolerates 200 - 1,500mm and experiences a dry season that lasts 5 - 9 months[, ].
Requires a sunny position[].Requires a well-drained soil, growing well in light to medium soils which can be shallow and of low fertility[]. Prefers a pH in the range 7 - 8, tolerating 6.5 - 8.5[].
Acacia tumida is a fast-growing plant when young, but is also a short-lived species, with a life-span of only 3 - 10 years[]. Sandplain forms of the plant can be coppiced successfully, and this lengthens their lifespan[].
This species can produce very heavy seed crops less than two years after planting and might have potential as a new human food in West Africa[]. Yields in excess of 100 kilos of seed per hectare have been attained from degraded, infertile sites within 2 - 3 years of planting[].
The seeds have been tested for toxicity and human trials have indicated that, at levels of up to 25% of the total diet, no anti-nutritional factors have been observed[].
The plant is grown as an ornamental[].
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[].
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[]. Australian Aborigines traditionally used Acacia tumida as a food source by roasting the mature seeds, grinding them into a flour, adding water to make a paste, then roasting the mix in coals to make a damper[]. The seedpods are 2.5 - 16cm long and 3 - 11mm wide; containing dark-brown to black, elliptic-oblong or pyriform seeds 4 - 9mm 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[].

An edible gum exudes from the trunk and branches[].

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 tumida has a shallow, wide-spreading root system that competes heavily with nearby crops and can reduce their yields[].
The tree can be used for sand dune fixation, erosion control, low windbreaks and as an ornamental[]

Other Uses

The bark can be used to make a string[].

The wood can be used for light construction[].
The wood makes a good fuel[, , ].

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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