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Ptaeroxylon obliquum (Thunb.) Radlk.

Protologue
Sitz.-Ber. Bayer. Akad. 20: 165 (1890).
Family
Rutaceae
Vernacular names
Sneezewood (En). Mwandara (Sw).
Origin and geographic distribution
Ptaeroxylon obliquum occurs from Tanzania and Angola south to South Africa.
Uses
The wood is highly valued for furniture and for poles in house building. In Mozambique it is favoured for making the keys of traditional xylophones, and for this purpose it is baked in an oven. It has also been used for railway sleepers and durable fence posts. It is suitable for heavy construction including marine works, heavy flooring, vehicle bodies, handles, sporting goods, implements, toys, novelties, precision equipment, carving, pattern making, vats and turnery. It is used as firewood.
The bark, the sawdust and the smoke from burning wood are used as a snuff against headache. Bark and wood infusions are considered remedies for rheumatism, arthritis and heart complaints. The wood resin is applied to warts and used to kill ticks on cattle. In Namibia tea made from the twigs is used against urinary complaints. Wood chips or dust are used to repel moths from clothes. In Tanzania the smoke from burning wood is used as traditional pesticide for stored grain.
Properties
The heartwood is rose-red to dark red, changing to orange-brown or golden brown on exposure, and distinctly demarcated from the pale grey, narrow sapwood. The grain is wavy, texture fine. Growth rings are distinct. The wood has a satiny lustre and a strong peppery smell; it contains oil that makes it very inflammable.
The wood is heavy, with a density of about 1000 kg/m³ at 12% moisture content. It air dries satisfactorily if drying is done carefully. The rates of shrinkage are moderate, from green to oven dry 3.6% radial and 5.6% tangential. Once dry, the wood is stable in service. At 12% moisture content, the modulus of rupture is 141–150 N/mm², modulus of elasticity 17,600–17,800 N/mm², compression parallel to grain 82–88 N/mm², shear 14–15 N/mm², Janka side hardness 13,700 N and Janka end hardness 13,650 N.
Taking into account its hardness, the wood is not difficult to saw, but it is difficult to work because of its wavy grain. However, it can be finished to a smooth and lustrous surface. The turning properties are excellent. Pre-boring before nailing is necessary. Gluing is difficult. The wood is extremely durable and resistant to termite, Lyctus and marine borer attacks. The wood dust is very irritating and may cause violent sneezing.
The wood and leaves contain chromones and other phenolic compounds. Some of these, methylalloptaeroxylin and perforatin A, showed antihypertensive effects. 7-Hydroxychromones have anti-oxidant activity. Ptaeroxylon obliquum lacks limonoids, which are commonly found in Rutaceae. An alkaloid isolated from the bark showed cardiac-depressant activity. Dichloromethane extracts of roots, leaves and stems showed moderate in-vitro antiplasmodial activity.
Botany
Dioecious, usually deciduous shrub or small to medium-sized tree up to 20(–45) m tall; bole often straight and cylindrical, up to 50(–120) cm in diameter; bark surface whitish grey, longitudinally fissured in large trees. Leaves opposite, paripinnately compound with 3–8 pairs of leaflets; stipules absent; petiole flattened, rachis usually ending in a short mucro; leaflets nearly sessile, very asymmetrically oblong-lanceolate to oblong-ovate, 2–6 cm × 0.5–3 cm, cuneate at base, notched to obtuse or slightly acuminate at apex, margin entire, densely short-hairy when young but glabrescent, pinnately veined with closely spaced lateral veins. Inflorescence an axillary contracted panicle up to 5 cm long. Flowers unisexual, regular, 4-merous; pedicel up to 6 mm long; sepals nearly free, ovate, c. 1 mm long, sparsely hairy; petals free, oblong, c. 5 mm × 1.5 mm, pale yellow; male flowers with 4 stamens c. 3.5 mm long and minute rudimentary ovary; female flowers with rudimentary stamens, ovary superior, laterally compressed, 2-celled, with rather short style and 2-lobed stigma. Fruit an oblong capsule c. 2 cm × 1 cm, notched at apex, reddish brown, reticulately veined, dehiscent with 2 valves, 2-seeded. Seeds with a large terminal wing, c. 16 mm × 6 mm.
Ptaeroxylon obliquum grows moderately fast: 40–100 cm/year in height under good conditions. In southern Africa trees flower in August–December when the trees are still leafless, usually just before new leaves develop. A flowering tree can be a spectacular sight. Fruits ripen about 2 months after flowering, and ripe fruits remain on the tree for some time.
Ptaeroxylon comprises a single species. It has been placed in Meliaceae and Sapindaceae and in more recent floras in Rutaceae. In the 1970’s it was excluded from Rutaceae into a separate family Ptaeroxylaceae, together with Cedrelopsis from Madagascar and later also Bottegoa from East Africa, but a more recent phylogenetic analysis of molecular data indicated that it is better included in an enlarged Rutaceae.
Ecology
Ptaeroxylon obliquum occurs in dry evergreen forest, often together with Podocarpus and Juniperus, and in bushland, from sea-level up to 2000 m altitude. It is drought tolerant and tolerates moderate levels of frost. It accepts well-drained sandy or rocky soils, but thrives best in shale or lime soils.
Management
Natural regeneration is often in forest margins, but saplings have also been recorded in Pinus plantations in South Africa. Regeneration may be abundant after severe opening of the forest canopy, and seedlings may cover the bare forest floor after disturbance. Seed can be collected just before the fruits dehisce. Pre-treatment before sowing is not necessary. The seed can be sown in an equal mixture of river sand and compost, and should be covered by a thin layer of sand. The germination rate of fresh seed is generally high, but seeds lose their viability rapidly, within a few months. One kg contains about 30,000 seeds. It is recommended to transplant seedlings when they have 3 leaves. Root suckers can also be used for propagation. Trees can be managed by coppicing, showing regrowth in about 75% of cut stems. Heart rot has been recorded as commonly present in logs.
Genetic resources and breeding
Although Ptaeroxylon obliquum is widespread, its distribution area is split up into 3 areas of different size: (1) near the coast in Angola and northern Namibia, (2) in north-eastern Tanzania (West Usambara Mountains), and (3) from Zimbabwe and southern Mozambique to eastern South Africa. This disjunct distribution can make this species liable to genetic erosion, especially in the first two areas, which are comparatively small and where Ptaeroxylon obliquum seems to be uncommon. It is a protected tree in South Africa, where in the past large numbers of trees were felled for timber and fuel, and where it has become scarce, particularly in larger sizes. In Mozambique it is in high demand for keys of traditional xylophones and has been subject to overexploitation.
Prospects
Ptaeroxylon obliquum is considered a valuable African timber tree, with great reputation for its durability. Its high density and hardness make it particularly suitable for specific local applications and less so for export purposes. However, it seems to be in need of conservation at present. The insecticidal properties of the wood deserve more research attention.
Major references
• Archer, R. & Reynolds, Y., 2001. Ptaeroxylon obliquum. [Internet] South African National Biodiversity Institute, Cape Town, South Africa. http://www.plantzafrica.com/ plantnop/ptaeroxylonobliq.htm. Accessed September 2007.
• 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.
• Mbuya, L.P., Msanga, H.P., Ruffo, C.K., Birnie, A. & Tengnäs, B., 1994. Useful trees and shrubs for Tanzania: identification, propagation and management for agricultural and pastoral communities. Technical Handbook 6. Regional Soil Conservation Unit/SIDA, Nairobi, Kenya. 542 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.
Other references
• Chase, M.W., Morton, C.M. & Kallunki, J.A., 1999. Phylogenetic relationships of Rutaceae: a cladistic analysis of the subfamilies using evidence from rbcL and atpB sequence variation. American Journal of Botany 86(8): 1191–1199.
• Clarkson, C., Maharaj, V.J., Crouch, N.R., Grace, O.M., Pillay, P., Matsabisa, M.G., Bhagwandin, N., Smith, P.J. & Folb, P.I., 2004. In vitro antiplasmodial activity of medicinal plants native to or naturalised in South Africa. Journal of Ethnopharmacology 92: 177–191.
• Geldenhuys, C.J., 1993. Observations of the effects of drought on evergreen and deciduous species in the eastern Cape forests. South African Journal of Botany 59(5): 522–534.
• 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.
• Langenhoven, J.H., Breytenbach, J.C., Gerritsma-Van der Vijer, L.M. & Fourie, T.G., 1988. An antihypertensive chromone from Ptaeroxylon obliquum. Planta Medica 54(4): 373.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• 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.E. & Gericke, N., 2000. People’s plants: a guide to useful plants of southern Africa. Briza Publications, Pretoria, South Africa. 351 pp.
• van Wyk, B.E., van Oudtshoorn, B. & Gericke, N., 1997. Medicinal plants of South Africa. Briza Publications, Pretoria, South Africa. 304 pp.
• White, F., 1990. Ptaeroxylon obliquum (Ptaeroxylaceae), some other disjuncts, and the Quaternary history of African vegetation. Bulletin du Muséum national d’Histoire naturelle, 4e série, section B, Adansonia 12(2): 139–185.
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. Ptaeroxylon obliquum (Thunb.) Radlk. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.