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 difficilis is a much-branched, multi-stemmed shrub 2 - 5 metres tall, or a tree that can grow 2 - 12 metres tall with a single, straight trunk up to half the total height of the tree[, , ]. 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.

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 - northeastern Western Australia, northern Northern Territory, northwestern Queensland

Habitat

An understorey species in open-forest and woodland dominated by eucalypts, also in low open-woodland and in open-scrub, usually in sandy or gravelly soils, often near creeks; at elevations up to 200 metres[, ].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Tree
Height	7.00 m
Growth Rate	Fast
Pollinators	Insects
Cultivation Status	Cultivated, Wild

Cultivation Details

Acacia difficilis is a plant of semi-arid to moist tropical climates in northern Australia, where it is found at elevations up to 200 metres. It grows best in areas where annual daytime temperatures are within the range 22 - 35°c, but can tolerate 13 - 42°c[]. When dormant, the plant can survive temperatures down to about 2°c, but young growth is more tender and can be severely damaged at 2°c[]. It prefers a mean annual rainfall in the range 650 - 1,100mm, but tolerates 450 - 1,500mm[].
Requires a sunny position. Found in the wild on light to medium-textured soils, preferably well-drained, and tolerating low fertility[]. Plants are tolerant of short periods with the soil inundated[]. Prefers a pH in the range 5 - 6.5, tolerating 4.5 - 7[].
A fast-growing tree (sometimes more than 2 metres a year when young) with a moderate life-span of 10 - 50 years. It produces seed heavily early in its life - flowering can commence before the tree is 12 months old[].
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[]. The seedpods of this species split open elastically at maturity, making
the seed difficult to harvest, but the seed is more easily cleaned than for other Acacia species[].
Plants do not always respond well to coppicing, especially when cut very low[].
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[].
Acacia difficilis is allied to, and often confused with, Acacia tumida. The two are difficult to distinguish in herbarium material in the absence of pods[].

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 70 - 140mm long and 3 - 4mm wide with black, oblong-elliptic seeds 5.5 - 7mm long, 2 - 4 mm 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 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 provide low shelter and erosion control in sandy soils[]. It is used by some mining companies in Australia in their mine rehabilitation activities[].
The plant flowers heavily and has potential as a source of pollen for bees[].

Other Uses

The wood may provide a source of small posts[].
The wood should be suitable for 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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