082 775 1224 / kerryn@cjmgrowers.co.za

The Largest Selection of Indigenous Species in any Nursery in KZN.

Trees, Shrubs, Aloes, Grasses and Ground Covers.

Acacia robusta

Acacia robusta subsp. robusta

(presently Vachellia robusta)

  • Ankle Thorn (E)

  • Robust Thorn (E)

  • Brack Thorn (E)

  • River Thorn (E)

  • Robust Acacia (E)

  • Splendid Acacia (E)

  • Splendid Thorn (E)

  • Broad-Pod Robust Thorn (E)

  • Oudoring (A)

  • Enkeldoring (A)

  • Brakdoring (A)

  • umNquawe (Z)

  • umNgamanzi (Z)

General

DESCRIPTION

  • A conspicuously tall, robust, upright Acacia, with handsomely gnarled, dark brown bark and a somewhat irregularly curved and dense, spreading crown of dainty, feathery leaves. The trees tend to branch quite high up, with nearly vertically spreading, upswept branches. During early spring, and often before the appearance of the new leaves, masses of ivory coloured, fragrant rich flowers adorn the tree, creating a cornucopia of delight for insects.

SA TREE

  • 183

FAMILY

  • Fabaceae or Leguminosae (Legume or pod-bearing family). This family is also divided into 3 subfamilies; mimosa or acacia subfamily, cassia and pea. Regarded as one of the largest, as well as economically significant families, its members have been cultivated since early times for their plethora of uses – as food, medicine, fodder, for practical use (tannins) and ornamental displays.

HABITAT

  • Commonly found from Somalia and Ethiopia, to Namibia and the northern and eastern parts of South Africa, where it prefers drier inland habitats. The trees are tolerant of a wide range of habitats, from woodlands, wooded and open grasslands, valley scrub, bushveld and along water courses, where the biggest specimens can be found.

Main Features

BARK

  • Dark grey-brown to almost black, very rough, with deep fissures. New twigs are hairless or finely woolly, without cracks, and the main stem is typically tall, straight, and often branches low down, with a diameter of 500-70 mm.

FOLIAGE

  • Briefly deciduous.

  • Bipinnately compound leaves, (40-85 mm long), carried on tiny, woody “cushions” that appear above the thorns, and are bunched tightly around the branchlets. Each leaf typically contains 3 – 6 pairs of pinnae, each bearing 11-27 pairs of leaflets (750-120 x 30-45 mm). The leaves are dark-green above, faintly paler below, with a more or less hairless leafstalk of up to 650 mm long. It has a visible furrow along the top. The thorns are straight (65-100 mm), white, paired at the base, and can sometimes be poorly developed.

FLOWERS

  • Creamy-white, globose “puffball” flowers, carried in clusters of up to 20 on “cushions” above the thorns. They are produced before or with the new leaves. (July-October).

FRUIT

  • A finely woody, more or less straight, tardily dehiscent pod (130-150 x 20-30 mm), maturing from grey to dark brown. There are no visible constrictions between the seeds. (November – June)

HEIGHT

  • 4-20 m

SPREAD

  • 2-6 m

Uses

MEDICINAL

  • Crushed leaves are applied topically as a snakebite remedy, while the pulverized roots are applied to abnormal swellings. A decoction of the roots is used to treat painful menstruation, sterility and bilharzia. An infusion of the stem bark is used against gonorrhoea, stomach aches and to bring relief from skin irritations.

PRACTICAL

  • The sapwood and heartwood are visibly demarcated, the latter being a beautiful pinkish bronze, while the sapwood is almost whitish. It has a moderately coarse, even, hard texture, is quite heavy, but is prone to warping and is brittle, with only moderate durability. It is also prone to attacks from borer and termites. Due to this, the wood is not hugely popular, but has occasionally been used in the construction of yokes, furniture and smaller implements. The pulping properties of the wood are said to be good. A good quality twine is made from the fibrous inner bark, and the bark is used to add colour to leather due to the presence of tannins. The wood is a good source of fuel and makes excellent charcoal.

WARNINGS

  • Care should be taken, especially on farms, as the leaves of most Acacias contain traces of the toxin Hydrogen cyanide, which can be fatal if ingested. The concentrations of the chemical increase during periods of drought or over-grazing. The trees also have an aggressively spreading root system, so should be planted clear of any permeant structures or pools.

Landscape

WILDLIFE

  • The flowers attract many insects, such as butterflies, beetles, wasps, moths, honeybees and more. The leaves are browsed by game and other smaller mammals, as well as farm animals, and the bark is eaten by rhino. Monkeys and baboons eat the young shoots and gum, the latter is also eaten by bushbabies and various insects. The seed pods are often parasitized by beetle larvae, and insectivorous birds can be seen foraging through the open pods to get to them. Seed eating birds will also be attracted by the open pods. The trees make excellent nesting sites for birds, as the dense, thorny branches offer protection from predators. It is also the host food plant for many Lepidoptera species (butterflies and moths).

ADVANTAGES

  • Highly adaptable and hardy, able to thrive even in frost-prone areas. The trees respond well to pruning, and can be trimmed into an excellent, thorny security hedge or screen. They provide lovely shade, especially on plantations, farms and large gardens, and are magnets for wildlife. Elegant, attractive garden and street trees, spectacular in full bloom. Popular as bonsai subjects. As with many Acacia species, the trees are host to nitrogen fixing soil bacteria, which form nodules on the roots. A symbiotic relationship occurs between the tree and these bacteria, as they are able to fix atmospheric nitrogen, which is essential for plant growth. This enhances the quality of the soil, to the benefit of the tree itself and other plants growing in its vicinity.

Cultivation

TOLERANCE

  • Once established, the trees can endure light to moderate frosts, and long periods of drought. They are resistant to strong winds.

GROWTH RATE

  • Moderate – fast. Under ideal growing conditions up to 1m per year can be expected.

LIGHTING

  • Full sun.

SOIL & WATER

  • The trees are tolerant of a wide range of soil conditions, from sandy, silty or slightly clay, but prefer deep, compost enriched, well-drained, loamy soil. They are water-wise trees, and have moderate water requirements, only requiring extra water during very hot periods in dry gardens.

PROPAGATION

  • Prior to being sown, the hard seedcoat needs to be broken or softened to speed up the germination process. This can be done by soaking the seeds for 12-24 hours in very hot, but not boiling, water. If they are not swollen by the next day, a small nick can be made in the seedcoat (be careful not to damage the embryo!) and the process can be repeated. Thereafter, the swollen seeds can be sown in a well-drained mixture of compost and river sand (1:2), and then covered with another thin layer of sand. Place in a warm, bright area and mist often. Germination is usually rapid, within 1-3 weeks. Seedlings can be transplanted into individual containers once they reach the two-leaf stage. Saplings can be planted out into open ground after one or two years and should be watered regularly until well established.

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CONTACT

082 775 1224

kerryn@cjmgrowers.co.za

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