Senegalia nigrescens

Senegalia nigrescens, the knobthorn, is a deciduous African tree, growing up to 18 m tall, that is found in savanna regions from West Africa to South Africa. The tree is resistant to drought, not resistant to frost and its hard wood is resistant to termites.

Description

A tree. It has knobs on the trunk. These have hooks. The tree grows 18-25 m high. It loses its leaves during the year. The leaflets are roundish and the leaves are twice divided. There are 3-4 pairs of divisions (pinnae) with one or two pairs of leaflets on each. The leaflets are 2 cm long by 1.5 cm wide. There are small hooked thorns on the branches near the leaves. The flowers have a sweet scent. They appear before the leaves. The whole tree is covered with creamy-white flowers. They are in spikes 9 cm long. The fruit is an oblong pod. It is green but turns a dark black or brown. It splits open after it falls off the tree.

Edible Uses

The leaves can be cooked and eaten as a vegetable. The gum is eaten as a snack.

Traditional Uses

The leaves can be cooked and eaten as a vegetable. The gum is eaten as a snack.

This uses section is brief — help expand it

Medicinal Uses

An ointment made from the roots has traditionally been used to treat convulsions.

Known Hazards

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.

Distribution

It is a tropical plant. It grows on flood plains in woodland. Plants are sensitive to frost. It grows in areas with a rainfall above 500 mm. It grows between 40-1,600 m above sea level. It is most common in the lowlands. It re-grows after fire. It can tolerate drought. It can grow in arid places.

Where It Grows

Africa, Botswana, East Africa, Eswatini, Malawi, Mozambique, Namibia, South Africa, Southern Africa, Sri Lanka, Swaziland, Tanzania, USA, Zambia, Zimbabwe,

Cultivation

Plants can be grown from seeds. The seeds can be soaked in cold water for 2 days then planted. They can be treated with hot water for a shorter time.

Propagation

Seed - easy to produce in the nursery the seeds are usually sown into seedbeds, but sowing directly into pots is also possible because of the high germination rate. Seedlings suitable for transplanting have been produced in less than 9 months. The seed of many 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.

Other Uses

The bark is a source of tannins. The inner bark can be used to make twine. The heartwood is dark brown, with light and darker streaks; it is distinctly demarcated from the narrow, whitish yellow sapwood. The grain is often irregular; texture moderately coarse and even. The wood is very heavy; very hard; it has very good natural durability, being extremely resistant to fungal, borer and termite attack. It is difficult to saw, even when green, and dulls tool edges; a good finish can be obtained with waxes and oil. The wood is used for parquet flooring, carving, turnery, fence posts, railway sleepers and mine props. It is occasionally made into furniture, although it is usually considered too heavy for this purpose. The wood is used as firewood and for charcoal production. Honey bees are particularly fond of the nectar from this plant, and produce a good quality honey from it.

Production

Trees are very slow growing. Trees can live for a few hundred years.

Other Information

They are a famine food.

Notes

There are about 1,350 Acacia species. Over 1,000 occur in Australia. This legume tree forms nodules. Also as Mimosaceae.

Synonyms

Also Known As

Ajam, Caia, Cananga, Chinanga, Chubunge, Gakaunga, Isinanga, Katopa, Mkunkhu, Mokoba, Muguhunga, Muhotohoto, Mukaya, Mukuu, Mukwamba-nziba, Munanga, Mungandu, Mupumbu, Muzoo, Nachiculia, Namuno, Nhlope, Umkhayamhlophe

References (15)

• Bircher, A. G. & Bircher, W. H., 2000, Encyclopedia of Fruit Trees and Edible Flowering Plants in Egypt and the Subtropics. AUC Press. p 4 (As Acacia nigrescens)
• Bunderson, W. T. et al, 2002, Common Agroforestry Species in Malawi. Malawi Agroforestry Extension Project, Pubication No. 46, Lilongwe. p 11 (As Acacia nigrescens)
• Fowler, D. G., 2007, Zambian Plants: Their Vernacular Names and Uses. Kew. p 33 (As Acacia nigrescens)
• ILDIS Legumes of the World http:www;ildis.org/Legume/Web (As Acacia nigrescens)
• Maguire, 1978, (As Acacia nigrescens)

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