Pavetta schumanniana

F.Hoffm. ex K.Schum.

Family : Rubiaceae
Common names : poison bride's bush (Eng.); gifbruidsbos (Afr.); Sawoti (siSwati); Tshituku ( Venda ); isiMbuzana (isiZulu)
Tree of the Year 2007

Pvetta schumanniana:Image Geoff Nichols
©Geoff Nichols

What? A poisonous (or poisoned) bride? Surely that is the starting-point of a third-rate horror movie, or a children's fairy tale! No, in fact the botanical version is a rather attractive small tree with very pretty white flowers.

Description
Shrub or tree often about 3.5 m tall, reaching 7 m in Kwazulu-Natal and 8.4 m in Tanzania. Leaves usually opposite, sometimes in whorls of 3, with interpetiolar stipules (small leaflike outgrowths on the stem between the bases of the leaves of a pair), egg-shaped, widest beyond the middle, 60-150 x 20-75 mm, shiny bright green with few rough hairs above, soft grey hairs below; tip rounded, margins not toothed, base tapering gradually into a short stalk.

Leaves and stipules

Flowers white, sweetly scented, in dense clusters on stalks, up to 20 mm long just below the leaves (September to February in South Africa ). Fruits round, buff to black, fleshy, up to 8 mm in diameter.

Conservation status
The poison bride's bush is very widespread and quite common. It is therefore no surprise that it is listed as Least Concern in Swaziland (Loffler & Loffler 2005), and not mentioned at all in South African literature on rare and threatened plants.

Distribution and habitat
Pavetta schumanniana grows in open woodland and bush clumps from northern Kwazulu-Natal, through Swaziland, Mozambique, the Lowveld of Mpumalanga and Limpopo Provinces into Zimbabwe, the Caprivi ( Namibia ) and far to the north in tropical Africa, from Tanzania to Cameroon. These places are characterized by hot summers and warm (certainly frost-free) winters, or by a relative lack of discernible seasons. Rainfall in the seasonal parts of the range of this species is mostlly in summer; in the more tropical areas it is monsoonal. The quantity of rain is moderate, as these areas are neither very dry nor moist enough to support rainforests.

Derivation of name and historical aspects
The genus name Pavetta is derived from a Sinhalese (Sri Lankan) vernacular name for a species of bride's bush-clearly the genus is very widespread. The specific epithet schumanniana commemorates Karl Moritz Schumann (1851-1904), an academic botanical colleague of the great Prof. Adolf Engler at Berlin. Schumann was a prolific author of botanical papers, but only an occasional collector. Pavetta schumanniana belongs to a group of mostly sub-shrubby plants, most of which are to be found in sandy parts of Angola. One relative which was only recently described as a separate species, and which comes from a somewhat more accessible locality, is P. vanwykiana Bridson, a Maputaland endemic whose range straddles the border between southern Mozambique and northern KwaZulu-Natal. Mabberley (2002) indicates that the genus Pavetta occurs throughout the Old World tropics, and contains some 400 species. However he cites the monograph of Bremekamp (1934) as his source; this is indeed the most recent treatment of the whole genus, but is held by subsequent workers to recognize too many species.

Ecology
The leaves of this tree are poisonous to stock (hence the common name), and cause a stock disease called gousiekte. In this form of poisoning, small doses of leaves cause heart failure (Coates Palgrave 2002). A few other species of Pavetta are also known to be poisonous, and act in the same way. Strangely, this only affects ruminants (cattle, goats, sheep); Codd & Voorendyk (1966) record a striking absence of reports of this kind of poisoning in horses, and that in experiments at Onderstepoort, researchers failed to induce anything untoward in small laboratory animals. Thanks are due to Prof. T.W. Naudé (Emeritus Professor of Toxicology at Onderstepoort) for confirming that poison bride's bush is harmless to humans; he informs me that in his experiments, large doses did produce symptoms in rats.

Like most species of Pavetta, the leaves of the poison bride's bush have black spots that are visible when the leaf is held up to the light. These are bacterial nodules, and the bacteria sheltering in them fix nitrogen from the air, releasing it in a form the host plant can use.

The white, scented flowers have all the features needed to attract moths, and one may deduce that they are moth-pollinated. Moths usually fly at twilight or at night, when almost any colour of flower other than white would be invisible. Scents serve to inform potential pollinators of the existence of a plant offering a reward nearby; that humans generally enjoy the aroma of these pheromones is a co-incidental benefit to gardeners.

FruitsThe black, fleshy fruits stand out against the green of the foliage and make them attractive to animals (presumably birds) which eat the fruits and spread the seeds. Fruits such as these are generally sweet to taste; for them to be poisonous would defeat the point of their being fleshy. However, readers of this account are warned against sampling the fruits of this tree; there are lookalikes which are not friendly.

Uses and cultural aspects
Tree-spotters will find the poison bride's bush at South African Tree No. 721, Zimbabwe No. 1130 in their lifer lists (Balkwill et al. 2004) or other reference books. (Incidentally, I firmly believe that all good tree-spotters should have a copy of this lifer list with them when looking at trees in the field. I find my copy invaluable for keeping track of the pictures I take of trees, but there are a thousand other uses for such a list.)

Despite (or possibly because of) being poisonous to stock, this tree has a large number of medicinal uses in Zimbabwe. These run from cures for coughs to treatments for infertility and venereal diseases in women.

Pavetta schumanniana. Copyright  Geoff Nichols
© Geoff Nichols

Growing Pavetta schumanniana

Several of the pictures accompanying this article show a tree growing in the Lowveld National Botanical Garden, Nelspruit. Visitors to Mpumalanga and the Kruger National Park are urged to make a detour to see this garden, which in this author's opinion is one of the country's best beauty spots. Those interested in seeing the creative use of poison bride's bush in a garden should look at the vegetation screening the gents' toilet just to the left of the main entrance (and very visible from the car park near the plant sales area). The main element of this screen is the tree in the picture below.

P.schumanniana in Lowveld NBG

This indicates that one possible use for Pavetta schumanniana in even quite small gardens is to hide an unattractive feature such as a wall or a shed. Other species of Pavetta are known to attract birds to the garden, and there is no reason to suppose that this one will not do so. Because the leaves are poisonous, trees should not be planted where they may tempt browsers.

The poison bride' s bush is well suited to warm areas with frost-free winters and moderate rainfall, such as the Lowveld of Mpumalanga. In areas where frost is experienced, it will require some protection, and may not survive excessive cold. Where the natural rainfall is low (say below about 500 mm p.a.) trees will require supplementary watering, which may suggest that you should grow hardier plants instead. That the natural habitat of this tree includes rocky outcrops and termite-mounds indicates that while it will survive in shallow, stony soil, it is well able to make good use of deeper, richer soils.

It appears that this is one of many quite desirable indigenous species that is not normally available from nurseries. Keen gardeners will therefore have to grow it from seed collected in the field (with the landowner's permission, please!). Geoff Nichols, the well-known Durban grower of all things indigenous (to whom many thanks for what follows), tells me that seed should be extracted from fresh fruits, washed and sown while still wet. Use a well-drained, sandy mixture of potting soil, and expect germination in two to four weeks-possibly a little faster if you keep the soil warm. Geoff believes that most species of Pavetta are mycorrhizal (require root fungi to grow, like orchids), and so seedlings will grow better if you add a small quantity of soil from around the roots of an existing bride's bush to the potting mixture. In any event, growth from germination to flowering is likely to be slow.

As there appears to be only one tree of this species "in captivity", nothing is known about its pests and diseases.

Other pavettas sometimes grown in gardens include P. lanceolata and P. gardeniifolia .

References and further reading

  • Balkwill, K., Boon, R., Coates Palgrave, M., Glen, H.F., Jordaan, M., Lötter, M., Schmidt, E. & Thomas, V. 2004. SAPPI Tree spotting lifer list. Jacana, Johannesburg.
  • Bremekamp, C.E.B. 1934. A monograph of the genus Pavetta L. Repertorium specierum novarum regni vegetabilis 37: 1-208.
  • Bridson, D. 1988. Pavetta. Rubiaceae. Flora of tropical East Africa 2: 618-686.
  • Coates Palgrave, M. 2002. Keith Coates Palgrave Trees of southern Africa, edn 3. Struik, Cape Town.
  • Codd, L.E. & Voorendyk, S. 1966. Plants which cause Gousiekte poisoning. Bothalia 8 Supplement: 47-58.
  • Glen, H.F. 2004. SAPPI What's in a name? Jacana, Johannesburg.
  • Kok, P.D.F. & Grobbelaar, N. 1984. Studies on Pavetta (Rubiaceae) 2. Enumeration of species and synonymy. South African Journal of Botany 3: 185-187.
  • Loffler, L. & Loffler, P. 2005. Swaziland tree atlas-including selected shrubs and climbers. Southern African Botanical Diversity Network Report No. 35. SABONET, Pretoria.
  • Mabberley, D. 2002. The plant-book, edn 2. Cambridge University Press, Cambridge.
  • Pooley, E.S. 1993. The complete field guide to trees of Natal, Zululand and Transkei. Natal Flora Publications Trust, Durban.
  • Schmidt, E., Lötter, M. & McCleland, W. 2002. Trees and shrubs of Mpumalanga and Kruger National Park. Jacana, Johannesburg.
  • Von Breitenbach, F. 1965. The indigenous trees of southern Africa. Government Printer, Pretoria.

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Author
Hugh Glen
Kwazulu-Natal Herbarium, Durban
February 2007

 

 

 

 

 

 


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