In a landscape characterised by grass and rock, all-year frost and drenching thunderstorms, Mundulea sericea stands out as the true star of the veld. In spring this silvery bush is covered in masses of purple flowers and insects and birds flutter amongst its branches. Its bark is similar to that of other species (e.g. Cussonia species) that need to protect their vascular tissue from frequent veld fires and frost. The leaves are delicate and soft, the flowers are large, beautiful, and pea-like. Throughout autumn, and often long into winter months, silvery silky pods clad the virgate (many long and slender) branches of the tree. The multitude of common names for this species alludes to its many uses and the degree of appreciation it has received in the past.
Attractive virgately branched shrub or a graceful small tree 0.5 - 7.5(-12) m high, usually single-stemmed with a bushy, much-branched crown. Bark on stem and branches are pale, corky and deeply furrowed-a fine contrast to the delicate silver-grey to light green foliage. Mundulea sericea plants growing in an evergreen habitat, devoid of fire, are usually tall, single-stemmed trees with a greenish yellow and smooth bark with almost imperceptible longitudinal fissures. They are strikingly different from the more frequently encountered form from whence the English common name, cork bush, is derived. Young branches are tough and pliant. Leaves are alternate, imparipinnate (having an uneven number of leaflets; thus having a single, terminal leaflet), covered with silky silver hairs, 80-100 mm long in 4-10 pairs of leaflets with an additional terminal leaflet (all ± 13 mm long), oval to lance-shaped, pale green. The flowers are showy and pea-like, carried in terminal clusters in a rich violet, mauve and lilac or even white. Flowers appear simultaneously with the new leaves in spring and early summer (October to February). The fruit are pods, ± 100 mm long and narrow, with thickened yellow-brown rims, becoming brown-grey as they mature, velvety hairy and may persist on the branches throughout winter. Fruits mature from November to April. Each pod contains 1-11 brownish-green, kidney-shaped seeds. The wood is light yellow, tough, and hard and produces a strong, unpleasant scent when worked.
Currently this species is not threatened.
Distribution and habitat
The genus Mundulea consists of ±15 species, widespread throughout Africa, Madagascar, Mauritius, India, Sri Lanka and Papua New Guinea. Only a single species, M. sericea, is found in southern Africa. This species occurs in South Africa, west of Botswana, Namibia and Angola, north to tropical Africa, and east to Madagascar, India, Sri Lanka and Papua New Guinea.
These plants prefer well-drained, deep sandy or gravelly soil. They are found in grassland, savanna or wooded grassland and thicket, often on rocky ridges, wooded hillsides, flats and sometimes near rivers.
Derivation of name and historical aspects
The name is derived from the Latin words Mundulea (neat/elegant) and the Latin word sericea (silver/silky) with reference to the compact, neat plant with its silver leaves when starting to sprout in springtime. Several of its African names mean "that which resist elephants" with reference to the strong, tough branches.
The flowers attract birds and insects. The Marico, short-billed and greater double-collared sunbirds visit the flowers for nectar. The Natal Barred Blue, Common Blue, Dusky Blue and Common Pea Blue butterflies use the cork bush for either feeding or breeding or both. Carpenter and other bees are attracted and are responsible for pollination. Wild (elephants, giraffes, eland and impala) and domestic (cattle and goats) animals browse on the leaves.
The fruit are poorly dehiscent and the seeds are scattered around the mother plant by browsing animals and birds.
Uses and cultural aspects
The pounded bark, leaves and sometimes seeds and roots are used for fish poisoning. Unlike many other plants used for this the fish are usually killed and not only just stunned by the poison. Leaves are stripped and pounded, placed in bags and thrown into the water. The dead fish are then collected for food at considerable risk, since there are cases where people have become ill after eating the poisoned fish. It is reported from east Africa that the poison is strong enough to kill small crocodiles. It is also said that strips of the bark were once tied round the legs of cattle whenever they were taken to the river to water in order to protect them from crocodiles. Surprisingly the bark and leaves are eaten by cattle, goats, elephants and antelope without any ill effect.
Rotenoids from the bark have commercially been used as an insecticide. This group of chemical compounds in the bark, leaves and seed is the active compound responsible for the fish poison. It is reported that the strength varies geographically. Rotenoids such as rotenone, deguelin and tephrosin, isolated from M. sericea, have been used as arrow poison and for inducing suicide. The bark is also said to be employed for homicidal purposes in parts of Africa.
To collect bark, stems are cut at ground level and the bark is stripped off as far as the branchlets. During the wet months the bark comes away quite easily and can be stripped off with the fingers. In winter, however, when the tree is not in an active growth stage, it has to be shaved off using a knife. The cutting of the stems at ground level does not kill the plant as it coppices freely (forms new branches from live plant parts).
In Kaokoland (northern Namibia) small branches are used as toothbrush sticks. The pounded leaves are mixed with lard and used as a hair dye.
Mundulea sericea is used in traditional medicine. The leaves are used by Zulus as an emetic to treat poisoning in both people and dogs. Infusions of the root are used to treat infertility. The powdered root is used in Venda in rituals to treat a married couple when the wife has had several miscarriages. During this ritual the couple are tied together with their backs against the tree.
Growing Mundulea sericea
Mundulea sericea is an attractive tree well worth introducing to a garden or used in various other horticultural ways to attract insects and birds. Due to its size it is ideally suited for small gardens. It is easily grown in well-drained soil enriched with some compost. Put boiling water in a container, add fresh seeds and soak for a day. Seeds that do not show signs of swelling may be rubbed on medium-grained sand paper just enough to scratch the surface and re-soaked. Sow in spring or summer in a well-drained seedling mixture (sand, compost and sifted soil in equal parts). Cover the seed with a 4-6 mm layer of seedling-mix and place the trays in a warm, semi-shaded position. Drench the trays with a fungicide to prevent fungal infections. Water regularly-the seeds should germinate in 2-6 weeks. When the seedlings reach the two-leaf stage (12-16 weeks after sowing), transplant them into nursery bags, pots or individual containers. Use sandy soil (or clay soil with 50% sand mixed in) with some well-rotted compost, and bone meal, taking care not to damage the long taproot. Seedlings and young trees usually transplant well. The tree is relatively slow-growing with a growth rate of 50-100 cm per year and can initially be used as a decorative shrub in a container. The growth rate increases as the tree ages. Feed with a seaweed fertiliser.
Depending on the climate, the cork bush may either be deciduous or evergreen. It is hardy, drought-resistant, and requires moderate water and full sun. It may be more frost-sensitive in the Highveld where it should be planted against a north-facing wall or in a warmer spot in the garden.
Mundulea sericea can be used as accent plant in a rock garden or a few clumped together make an attractive composition. It is an excellent choice for a container or grown as a bonsai. Plants grown together and pruned make an interesting indigenous hedge. The root-system is not aggressive.
References and further reading
- Coates Palgrave, K. 1991. Trees of southern Africa. Struik Publishers, Cape Town.
- Coates Palgrave, M. 2002. Keith Coates Palgrave Trees of southern Africa, edn 3. Struik, Cape Town.
- Curtis, B.A. & Mannheimer, C.A. 2005. Tree Atlas of Namibia. National Botanical Research Institute, Windhoek.
- Germishuizen, G. & Fabian, A. 1997. Wildflowers of northern South Africa. Fernwood Press, Vlaeberg, Cape Town.
- Greenway, P.J. 1936. Mundulea fish poison. Bulletin of miscellaneous information, No. 4 Kew Bulletin 1936: 245-250.
- Joffe, P. 1993. The gardener's guide to South African plants. Delos, Cape Town.
- Joffe, P. 2003. Creative gardening with indigenous plants : a South African guide. Briza, Pretoria.
- Kruger, T.J. 1973. Bome, struike en rankplante.
- Leistner, O.A. (ed.) 2000. Seeds plants of southern Africa : families and genera. Strelitzia 10. National Botanical Institute, Pretoria.
- Palmer, E. & Pitman, N. 1972. Trees of southern Africa, vol. 1. Balkema, Cape Town.
- Pole Evans, I.B. 1931. Mundulea suberosa. The Flowering Plants of South Africa 11: t. 406.
- Schmidt, E., Lötter, M. & McLeland, W. 2002. Trees and shrubs of Mpumalanga and Kruger National Park. Jacana, Johannesburg.
- Setshogo, M.P. & Venter, F. 2003. Trees of Botswana : names and distribution. Southern African Botanical Diversity Network Report No. 18, SABONET, Pretoria.
- Smith, C.A. 1966. Common names of South African plants. Memoirs of the Botanical Survey of South Africa No. 35.
- Van Wyk, B. & Malan, S. 1997. Field guide to the wildflowers of the Highveld. Struik, Cape Town.
- Van Wyk, A.E. & Van Wyk, P. 1997. Field guide to trees of southern Africa. Struik, Cape Town.
- Van Wyk, B.-E. & Gericke, N. 2000. People's plants: a guide to useful plants of southern Africa. Briza, Arcadia.
- Van Wyk, B.-E., Van Heerden, F. & Van Oudtshoorn, B. 2002. Poisonous plants of South Africa. Briza, Arcadia.
- Van Wyk, P. 1994. Fieldguide to the trees of the Kruger National Park. Struik, Cape Town.
- Venter, F. & Venter, J.-A. 2007. Making the most of indigenous trees. Briza, Arcadia.
- Watt, J.M. & Breyer-Brandwijk, M.G. 1962. The medicinal and poisonous plants of southern and eastern Africa, edn 2. Livingstone, Edinburgh and London.
S.P. Bester & A. Grobler