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: Creek Wattle

General Information

Acacia rivalis is a shrub or a tree with a bushy, domed crown; it can grow 3 - 5 metres tall[]. The stem can be unbranched for about 1 metre before dividing, or can divide at or near ground level into a few to many stems. The main stems are more or less straight, around 7 - 10cm in diameter[]. 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. The seed is considered to have potential as a commercial food source; the plant has potential for commercial wood production; and the plant was at one time harvested on a commercial basis in South Australia for its gum[]. An attractive plant, it is suited for cultivation as an ornamental or for amenity planting in dry inland areas[].

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 - South Australia

Habitat

Tall shrubland on ridges and rocky shaly hills or along watercourses, in shallow calcareous loam[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Shrub
Height	4.00 m
Growth Rate	Medium
Pollinators	Insects
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Acacia rivalis is a native to the semi-arid and arid regions of temperate southern Australia, where it can be found at elevations up to 750 metres. It grows best in areas where the mean maximum temperature of the hottest months can reach 30 - 35°c, and the mean minimum in the coldest month can fall to 2 - 5°c. The plant can experience moderate frosts, down to around -5°c for short periods. Mean annual rainfall can vary from 150 - 400mm, with a dry season of 3 - 12 months[].
Requires a sunny position and a well-drained soil[].
The plant has a moderate to fast rate of growth, though it is relatively short-lived with a life span of probably 15 - 20 years[].
In one trial site on a clay soil plants were around 2 metres tall when two years old[].
Plants do not sucker, and only coppice weakly, but regenerates abundantly by seed following fire[].
The seedpods ripen over about a year, maturing between mid Spring and early Summer. Ripening oods and flowers are often found together on the same plant. The plant can produce large quantities of seed[].
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[].

Edible Uses

Seed - cooked[]. Ground into a flour[]. The seedpods are up to 16cm long and 4 - 4.5mm wide, with oblong to elliptic, black seeds 5 - 6mm 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[].

Other Uses

Moderate quantities of a gum exude naturally from the stems and branches[].

The wood has potential as a commercial source of material for the pulping and reconstituted wood industries[].

Propagation

Seed - best sown as soon as it is ripe in a sunny position in a warm greenhouse[].The dried 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. Sow the seed in Spring in a greenhouse. As soon as the seedlings are large enough to handle, prick them out into individual pots and grow them on in a sunny position in the greenhouse for their first winter. Plant them out in late spring or early summer, after the last expected frosts, and consider giving them some protection from the cold for their first winter outdoors.
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[].