Diplorhynchus condylocarpon (Müll.Arg.) Pichon
Common names: Rhodesian rubber tree, horn-pod tree, wild rubber (Eng.); horingpeultjieboom, horingpeulbos, melkbos (Afr.); mutowa (Shona); tsowa (Tsonga); ntsowa, mulya (Tswana); muthowa (Venda)
SA Tree No: 643
Diplorhynchus condylocarpon grows either as a shrub or as a small, graceful tree with drooping branches. Although it is seldom found in gardens, the sweet jasmine-like scent of the flowers attracts a variety of insects and birds. The tree has many uses throughout its distribution range.
Diplorhynchus condylocarpon grows as a shrub or small, deciduous, multi-stemmed tree up to 8 m high, with grey-brown to blackish bark. The trunk is covered with small knob-like outgrowths (lenticels) and becomes scaly with age, cracking into small segments.
It has a wide-spreading, sparse crown with long, slender, drooping branches and shiny, opposite leaves. The leaves are light to dark green, leathery and smooth, 30-70 x 19-50 mm.
All parts of the plant contain milky sap. The flowers are white- to cream-coloured, very small and fragrant, and are borne in terminal sprays. They usually appear with the new leaves from September to December. Two hard, woody, dark brown fruits (follicles) with pointed tips and speckled with white dots (lenticels) develop from some flowers. The fruits ripen between March and September and carry 2-4 compressed, winged seeds.
The horn-pod tree is not rare or threatened and is widely distributed, but is never common in local populations.
Distribution and habitat
Diplorhynchus condylocarpon is distributed in tropical Africa in Angola, Zambia, Zimbabwe, Malawi and Mozambique, and in southern Africa in Namibia, Botswana and South Africa (Limpopo, North-West, Gauteng and Mpumalanga provinces). It grows in warm, dry, frost-free situations, on rocky slopes and in deep sandy soil in open woodland.
Derivation of name and historical aspects
The name of this species is derived from various Greek words: the generic name Diplorhynchus from diplo (double) and rhynchos (beak), referring to the paired, beak-like fruit; the specific name condylocarpon from kondylos (knuckle or prominence) and karpos (fruit) with reference to the shape of the fruit.
This is a monotypic genus, one species representing the entire genus. Previously, several species were recognised, but the plants are very variable in many characters, and it seems impractical to subdivide this complex. All previous names were therefore placed in synonymy.
Diplorhynchus condylocarpon is reported to be fire-resistant and apparently even withstands repeated burning. In the wild it is known to attract insects such as butterflies and bees, as well as birds. It is one of the favourite browse plants of the black rhino, and is also heavily browsed by elephants. The fruits are eaten by small antelope and are apparently the favourite food of rhinos.
Diplorhynchus condylocarpon contains milky latex, which forms a soft, rubber-like substance sometimes used as bird-lime. It is also applied to the hides of drums to improve the quality and tone of the sound. The latex has even been used to repair the cracked sump of a car as well as punctures in bicycle tyres. It is also used as a remedy for screw-worm. Some tribes use it as a glue to stick feathers onto their arrows.
Leaves are used in traditional medicine. The Wemba tribe chew the leaf together with those of some other plants, breathe into the ears and nostrils, and place the chewed material on the forehead of a patient to relieve a headache and an upset stomach. Roots are also used in traditional medicine. A strong suspension of the roots has been used to relieve blackwater fever. An infusion of the root is recorded as a treatment for diarrhoea.
Some tribes plant the tree because of its aroma, and use it as a snake-bite remedy and an emetic. The vapour from the fruit and roots boiling in water is inhaled to relieve a chronic cough and pulmonary tuberculosis. The latex has also been used as a wax for removing hair.
The wood is pale brown, fine-grained, hard and quite heavy, and is suitable for making various small carved ornaments, as well as utensils such as spoons. If large enough trunks can be obtained, it is even used for making furniture. The wood is said to be very attractive when polished. Branches are used for assegai and arrow shafts and for fuel. In Zambia, the outer bark is used as a substitute for tobacco, and pounded bark as a wound dressing. The wood is also used for making strong fire-sticks.
In the past, the horn-pod tree has also been used for its bark fibre from which a cloth was woven or knotted (into pieces as large as blankets), known as gupo. These were traditionally worn by women in Zimbabwe.
Growing Diplorhynchus condylocarpon
The horn-pod tree can be established successfully as long as it is planted in areas coinciding with its natural distribution range. Because of its deciduous nature, it is not favoured by many gardeners, but this attribute makes it ideal around the home for those places that are cold in winter and hot in summer.
This medium-sized tree grows to a height of 8 m, with the crown also spreading to 8 m. If planted too close to other trees or large shrubs, it tends to grow as a tall, slender tree, with the crown hardly spreading. Young plants have to be sheltered from frost, and established plants have to be grown in full sun and watered moderately. The horn-pod tree has a moderate growth rate.
This species has a high potential for use in gardens and landscaping because of its small size and appealing growth form. However, like many other sandveld species of the northern parts of South Africa, including Burkea africana, Combretum seyheri and Ochna pulchra, it is very difficult to grow. Plants are not stocked by any of the nurseries that were contacted. Only a few have tried to build up stock but, owing to the extremely sensitive roots, the young plants do not keep well in bags, making it economically unviable for nurseries to keep them. The seed must be fresh, sown in a sandy seedling medium that drains very well. Do not over-water the seedlings as they are easily attacked by fungi. Young plants can be transplanted in bags. Usually the roots rather than the stem seem to be the most sensitive to cold if kept in containers. Plants established directly in the ground tend to fare better and have higher survival rates when young. The tree is also reported to have been propagated from truncheons. Many accounts that refer to its use as fencing-poles mention that poles of this species take root and start to grow.
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Plant Type: Shrub, Tree
SA Distribution: Gauteng, Limpopo, Mpumalanga, North West
Soil type: Sandy
Flowering season: Spring, Early Summer
Flower colour: White, Cream
Aspect: Full Sun
Gardening skill: Average