Acacia siliquastrum Lag.

Prosopis chilensis is a small to medium sized tree up to 12 m in height and 1 m in diameter; bark brown, fissured; spines a pair, stout, yellow, glabrous; root system reportedly shallow and spreading. The leaves are compound, each with numerous leaflets along several pairs of pinnae. P. chilensis has 10-29 leaflets per pinnae and no more than two pairs of pinnae per leaf. The leaflets are about 1 cm apart. The flowers are greenish-white to yellow, abundant and occur in spike-like racemes. The pods are beige to off-white, about 15 cm long and 15 mm wide. The pods have a tendency to be rolled up along the axis. Seeds many, bean-shaped, oblong, 6-7 mm long, flattened, brown, each in 4-angled case.

Flowering regularly in spring and sometimes sporadically again in late summer and like other members of the genus Prosopis, it is diploid, self-incompatible and insect pollinated.

Found in sandy, alkaline soils and has proved to be salt tolerant.

P. chilensis is found in the arid and semi-arid regions with ground water of between 3 and 10 m below the surface, such as drainage channels along ground water sinks. It has been observed to grow in seawater salinity. It is a common ruderal weed, coming up singly and in groups along roadsides, round habitations, on refuse dumps and in other disturbed habitats.

In South Africa and South West Africa (Namibia), P. chilensis was introduced in 1912 by Dinter (a botanist), who distributed it widely as a fodder and shade tree over the next few years. In other countries such as the Sudan, it has been introduced by foresters to combat desertification and is now a widespread weed in most areas of western and central parts of the country.

Seed propagation has largely been used to propagate P. chilensis. Seeds are difficult to extract from the gummy pulp. P. chilensis pods can be ground in a meat grinder after drying pods in an oven overnight at 52 deg. C. This will also serve to scarify the seeds for good germination. Seeds can also be scarified with a file, knife or conc. sulphuric acid before planting. Outstanding trees have been cloned using rooting or cutting techniques.

Spacing of 6 x 6 m to 13 x 13 m would be ideal. Mechanical and chemical weed controls are needed to maximize growth. Due to abundant growth of basal branches, pruning at the age of 4- 6 years is necessary to allow animal access to the forage which falls from the trees.

Twig girdling insects (Oncideres spp.) causes minor damage to this tree. An un-described disease causes the terminal shoots to die. This necrosis gradually spreads downward and eventually may kill the entire tree.

Seed storage behaviour is orthodox; viability can be maintained for several years in hermetic storage at room temperature with 5-9% mc. There are about 36 000 seeds/kg.

Erosion control: P. chilensis is a candidate for erosion control and soil stabilization in arid lands, due to its deep rooting habit. Shade or shelter: P. chilensis planted as a hedgerow provides shade for fruit trees, field crops and to the homesteads. Shade provided in paddocks not only eases the lot of farm animals but also substantially increases meat production. Nitrogen fixing: Like other legumes, P. chilensis is able to fix atmospheric nitrogen in its root nodules. Ornamental: Due to its broad, rounded, open head of bright green foliage supported by gracefully arched spineless branchlets, its rapid growth and large size, P. chilensis has widely been used as an ornamental tree in Argentina, Arizona and California. Boundary or barrier or support: P. chilensis could possibly be used to an advantage as barrier plant to form stock-proof hedgerow. If selectively coppiced on a cutting rotation of five years, such hedgerows would, by way of bonus, also provide a perennial source of pods and firewood. Intercropping: Grasses and other plants have been said to grow better in association with P. chilensis, benefiting from shelter, humus and nitrogen which it fixes. When integrated into an agroforestry system, shelter-belts, avenues and groves of P. chilensis would make a major impact on the micro-climate as well as provide various products and services. The pods could be collected and crushed, or animals with access to the pods should not be allowed to roam freely so as to minimize the risk of uncontrolled spread.

Food: The pods are eaten by the native people (Northern Argentina), especially as a ground flour. Fodder: The pods and not the leaves are readily eaten by livestock. They have as high as 35% sugar content and contain 10-12% crude protein. Seeds are sometimes ground in a concentrate for animal feeds. Large trees, 40 cm in basal diameter and 7 m in canopy diameter, may produce 40 kg of pods under optimal condition. Apiculture: P. chilensis is a good source of nectar and pollen. A pale amber-coloured honey of medium density and good flavour is produced in abundance. Its flowering season is short and therefore it is not able to support a large swarm of bees throughout the year. Fuel: When burnt P. chilensis ignites readily, has a high calorific value, emits intense heat, makes enduring embers and leaves little ash. The wood makes good charcoal and could be exploited commercially to supply industrial and domestic demand using portable kilns. Fibre: Wood yields sulphate pulp for writing and printing works. Timber: P. chilensis wood is relatively dense (about 700-800 kg/m³). It is valued for furniture, doors, cobblestones and parquet floors. The wood has a low volumetric shrinkage hence joints in furniture have much less tendency to open during conditions of changing humidity. Gum or resin: The bark exudes an amber-coloured, translucent gum similar to gum arabic used in mucilage and an ingredient in medicine.