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The Mopane Tree (Colophospermum Mopane)

Introduction

The Mopane tree (Colophospermum mopane) or Omusati in the local Oshiwambo language, dominates the eastern reaches of the Kaokoveld as well as the sandveld as far as the Etosha Pan. It is so widespread in the north-west of Namibia that a region in Owambo is named after it. One of the principal trees in the southern tropics of Africa. It is the soil structure that determines whether mopane grow into fully-fledged trees or remain as multi-stemmed shrubs.

Mopane's generic name Colophospermum is Greek, which means 'oily seed' and it refers to the sticky, kidney-shaped, flat brown seeds. When crushed, both seeds and leaves smell strongly of turpentine. All parts of the mopane are resinous, and burn even when green. The species name, mopane, is taken from the local name for the tree. The genus Colophospermum only occurs in Africa and there is only one species in the genus. The mopane is in the pea family (Fabaceae). This huge and important family is further divided into three subfamilies; the mopane lies within the Caesalpinioideae. Colophospermum  mopane can be confused with the small false mopane, Guibourtia conjugata in areas where they co-occur in the far northeast corner of South Africa, although the seeds of the false mopane are not convoluted or resinous and the bark not as rough and fissured. The leaves also do not have the tiny spike-like remnant of the third leaflet.

Mopane leaves

Description

The mopane can be a shrub or a tall tree up to 30 m in the northern part of its range, depending on soil conditions and water availability. It has a tall, narrow crown. The compound leaves are divided in two so that the leaflets resemble butterfly wings or a camel's foot. There is a tiny point at the join of the two leaflets which is the remnant of a third, terminal leaflet. Crushed leaves have a turpentine odour. It is a deciduous (sometimes semi-deciduous) tree with lovely autumn and spring colours. Sprays of small, green flowers appear in December and January.

These are followed by pods which ripen between April and June and are flat and somewhat kidney-shaped. They change from green to light, finely speckled brown. The flat seeds inside are sticky from resin exuded by glands which cover them. The strange appearance of the seeds is from the convolutions in their surface. Some might say they resemble tiny, flat mottled-brown brains! The greyish brown bark is very deeply fissured in vertical fissures. It has a rough, ropey appearance and is very distinctive.

Distribution and habitat

Habitat area

Colophospermum mopane grows in hot, dry, low-lying areas, 200-1150 m, in the far northern parts of South Africa, into Zimbabwe, Mozambique, Botswana, Zambia, Namibia, Angola and Malawi. It is found growing in alkaline (high lime content) soils which are shallow and not well drained. It also grows in alluvial soils (soil deposited by rivers). In South Africa and adjacent areas of Botswana and Zimbabwe, the trees tend to vary between 4 and 18 m, often called mopane scrub, but also sometimes taller and forming woodland, while further north the trees are taller and form tall woodlands referred to as cathedral mopane. I recall visiting Botswana's Okavango Delta and encountering miles of lush mopane woodlands of great height, interspersed with waterlily-filled ponds, quite different to the familiar mopane scrub of the south. This tree does not grow well outside of suitable hot, frost-free, summer rainfall areas. However, it would be tolerant of poor, alkaline soils.

Ecology

If you were to travel through areas of mopane woodland in the heat of the day and wished to stop and rest in the shade, you would have trouble finding any! To save water, the leaflets fold together and present the smallest surface area toward the sun, thereby reducing exposure of the leaf surface. This also prevents much shade from being cast. The mopane is often deciduous in winter, possibly another adaptation to drought, since winters are not very cold in the lowveld, but they are dry. The lovely reddish new leaves only emerge in October in anticipation of the first rains. Game animals, particularly elephants, enjoy the protein-rich leaves and pods. Elephant pressure may be part of the reason for the stunted appearance of some areas of mopane scrub. Domestic animals find the pungent leaves unpalatable at first but will feed on them once used to the taste, and their meat and milk is apparently untainted with a turpentine flavour. The young leaves have a higher protein content and are more palatable, but even the dry, fallen leaves yield valuable protein for stock and game.

Hole-nesting birds like the mopane woodlands as they offer many nesting sites. Mopane tree is picked off the leaves by people and baboons. This is a sweet-tasting, waxy cover on the juvenile stage of a sap-sucking insect known as the mopane psyllid, Arytaina mopani. The well-known mopane worm, which is the large caterpillar of the Imbrasia belina emperor moth, the Gonometa moth and the caterpillar of the foxy charaxes butterfly, Charaxes jasius saturnus, feed on the mopane. The tiny mopane bee, Plebina denoita, which many know from its attempts at crawling into one's eyes, ears and nose, produces a small amount of edible honey. They make their nests in hollow trunks with a small wax tube as the opening to the outside. Mopane seed pods do not split open of their own accord and the seeds can germinate while still in the pod.

Uses

In summer the leaves of Colophospermum mopane are fed on by swarms of fat, dark greyish mopane worms, which can reach almost 10 cm long. These are rich in protein and are eaten by people, either roasted or dried. The sale of dried mopane worms is an important income source for many people, creating a local economy. Other traditional uses of the mopane tree include the making of houses and kraal fences, the chewing of twigs as tooth brushes, the use of bark to make twine and for tanning, and the use of leaves for healing wounds. The hard, reddish heartwood timber was used to make railway sleepers and as props for mining activities. This is one South Africa's heaviest timbers and is apparently difficult to work because of its hardness, but this also makes it termite-resistant, therefore a popular choice for fence posts and flooring. The Gonometa moth caterpillar spins silken cocoons which are harvested as wild silk to make cloth.

Growing Colophospermum mopane

The mopane has a rather limited horticultural potential in areas outside of the hot, summer rainfall areas of South Africa. It is not tolerant of cold and frost. It would be a good addition to a wildlife garden and for adding autumn and spring interest. It is best grown from seed. Seeds can be removed from ripe pods or sown in the pod. Removing the seeds from the pods does speed up germination but needs to be done carefully. They should be sown in flat seedling trays in river sand. Place the seeds on the sand surface. Keep the trays moist so that the seeds can absorb water to germinate. Once the seeds have germinated they will be susceptible to infection from damping-off fungi, therefore the amount of water should be reduced. It also helps to use clean new river sand, sterilised if possible. The seedlings are initially slow growing but the growth rate speeds up once a height of about 200 mm is reached. Transplanting will need to be done with care, and you should try to avoid damaging the roots. Use loamy soil with some sand and compost added, in black nursery bags, and water well after the transplanting operation

References

1. http://www.krugerpark.co.za/africa_mopane.html
2. https://www.tandfonline.com/doi/abs/10.2989/10220119.2014.899513
3. http://www.softschools.com/facts/plants/mopane_facts/1282/
4. ESTERHUYSE, N., VON BREITENBACH, J. & SÖHNGE, H. 2001. Remarkable trees of South Africa. Briza Publications, Pretoria.
5. https://archive.org/details/nje-A-volume1-cunningham/page/n3