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Zanthoxylum davyi (Verd.) P.G.Waterman

Protologue
Taxon 24: 363 (1975).
Family
Rutaceae
Synonyms
Fagara davyi Verd. (1919).
Vernacular names
Knobwood, forest knobwood, knobthorn (En).
Origin and geographic distribution
Zanthoxylum davyi occurs in Zimbabwe, eastern South Africa and Swaziland.
Uses
The wood is used for handles, walking sticks and fishing rods. It is suitable for heavy construction, heavy flooring, joinery, interior trim, vehicle bodies, furniture, cabinet work, mine props, ladders, sporting goods, agricultural implements, toys, novelties, musical instruments, boxes, crates and turnery.
The stem bark is used to treat cough, cold, boils, pleurisy, toothache and snakebites. The prickles are applied to infected wounds, the leaves to treat chest pain and as a poultice to heal sores, and the roots to treat mouth ulcers and sore throat, and as a tonic and aphrodisiac. The prickle-bearing protuberances on the bole have been used by children as toys, and have also been made into pipes.
Properties
The heartwood is pale greyish brown, often with greenish markings, fairly distinctly demarcated from the greyish sapwood. The texture is fine and even. Growth rings are distinct.
The wood is heavy, with a density of 830–930 kg/m³ at 12% moisture content. It air dries fairly rapidly in small dimensions, but larger boards are liable to surface checking. The rates of shrinkage are moderate, from green to oven dry 4.1% radial and 8.4% tangential.
The wood is strong and elastic. At 12% moisture content, the modulus of rupture is 128–140 N/mm², modulus of elasticity 15,700 N/mm², compression parallel to grain 55–57 N/mm², shear 15–17 N/mm², Janka side hardness 9210–10,450 N and Janka end hardness 9790–11,260 N.
The wood is fairly easy to saw and work in spite of its hardness. The polishing, gluing and bending properties are satisfactory. The wood is only moderately durable and susceptible to Lyctus attack. The heartwood is resistant to impregnation by preservatives.
The stem bark yielded 5 benzophenanthridine alkaloids. One of these, chelerythrine, is well known for its antimicrobial and anti-inflammatory properties. Crude stem extracts showed pronounced antibacterial activity against Escherichia coli, Shigella spp., Salmonella typhi and Streptococcus pyogenes, but no activity against Staphylococcus aureus.
Botany
Dioecious, medium-sized tree up to 30 m tall; bole usually straight and cylindrical, up to 60 cm in diameter, with conspicuous woody, prickle-bearing protuberances, sometimes slightly fluted at base; bark pale grey in younger trees to dark brown in older ones; twigs glabrous, armed with up to 5 mm long prickles. Leaves alternate, imparipinnately compound with (5–) 7–13 leaflets, up to 30 cm long; stipules absent; rachis channelled above, often with small prickles; leaflets opposite, sessile, slightly asymmetrically oblong to lanceolate or narrowly elliptical, 2–7(–10) cm × 1–3 cm, cuneate to obtuse at base, shortly acuminate and slightly notched at apex, margin finely toothed, glabrous, with glandular dots confined to the margin, pinnately veined with numerous lateral veins. Inflorescence a terminal panicle up to 6 cm long, with flowers in clusters. Flowers unisexual, regular, 4-merous, small; pedicel 1–1.5 mm long; sepals nearly free, c. 0.5 mm long; petals elliptical, c. 2.5 mm long, greenish yellow; male flowers with 4 stamens, ovary rudimentary; female flowers with superior, globose ovary and short style. Fruit a globose follicle c. 5 mm in diameter, glandular pitted, dehiscent, 1-seeded. Seed globose, c. 3 mm in diameter, black and shiny.
Zanthoxylum davyi flowers from October to January and fruits ripen about 3 months later.
Zanthoxylum is pantropical and comprises about 200 species, with tropical America being richest in species. Mainland Africa harbours about 35 species, whereas about 5 species are endemic to Madagascar.
Ecology
Zanthoxylum davyi occurs in forest and forest patches, from coastal regions to mountainous areas; it is locally common in montane forest.
Genetic resources and breeding
The conservation status of Zanthoxylum davyi in South Africa is indeterminate, but in Zimbabwe it is considered endangered.
Prospects
The information on Zanthoxylum davyi is too limited to judge its prospects as a commercial timber tree under sustainable exploitation management. However, stands of large trees are probably too scarce, and an inventory is needed.
The medicinal properties deserve more attention because of the claimed antimicrobial activities, which have been confirmed by pharmacological research.
Major references
• Bolza, E. & Keating, W.G., 1972. African timbers: the properties, uses and characteristics of 700 species. Division of Building Research, CSIRO, Melbourne, Australia. 710 pp.
• Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
• Palmer, E. & Pitman, N., 1972–1974. Trees of southern Africa, covering all known indigenous species in the Republic of South Africa, South-West Africa, Botswana, Lesotho and Swaziland. 3 volumes. Balkema, Cape Town, South Africa. 2235 pp.
• Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan, 248 pp.
• Tarus, P.K., Coombes, P.H., Crouch, N.R. & Mulholland, D.A., 2006. Benzo[c]phenanthridine alkaloids from stem bark of the Forest Knobwood, Zanthoxylum davyi (Rutaceae). South African Journal of Botany 72(4): 555–558.
Other references
• Grace, O.M., Prendergast, H.D.V., Jäger, A.K. & van Staden, J., 2002. Bark medicines in traditional healthcare in KwaZulu-Natal, South Africa: an inventory. South African Journal of Botany 69(3): 301–363.
• Kelmanson, J.E., Jäger, A.K. & van Staden, J., 2000. Zulu medicinal plants with antibacterial activity. Journal of Ethnopharmacology 69: 241–246.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• Obi, C.L., Potgieter, N., Randima, L.P., Mavhungu, N.J., Musie, E., Bessong, P.O., Mabogo, D.E.N., & Mashimbye, J., 2002. Antibacterial activities of five plants against some medically significant human bacteria. South African Journal of Science 98(1–2): 25–28.
• van Vuuren, N.J.J., Banks, C.H. & Stohr, H.P., 1978. Shrinkage and density of timbers used in the Republic of South Africa. Bulletin No 57. South African Forestry Research Institute, Pretoria, South Africa. 55 pp.
• van Wyk, B. & van Wyk, P., 1997. Field guide to trees of southern Africa. Struik Publishers, Cape Town, South Africa. 536 pp.
Author(s)
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands


Editors
D. Louppe
CIRAD, Département Environnements et Sociétés, Cirad es-dir, Campus international de Baillarguet, TA C-DIR / B (Bât. C, Bur. 113), 34398 Montpellier Cedex 5, France
A.A. Oteng-Amoako
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana
M. Brink
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
J.R. Cobbinah
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

Correct citation of this article:
Lemmens, R.H.M.J., 2008. Zanthoxylum davyi (Verd.) P.G.Waterman. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.