Zanthoxylum heitzii (PROTA)

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Plant Resources of Tropical Africa
List of species

General importance Fairytale bookmark gold.svgFairytale bookmark gold.svgFairytale bookmark gold.svgGood article star.svgGood article star.svg
Geographic coverage Africa Fairytale bookmark gold.svgGood article star.svgGood article star.svgGood article star.svgGood article star.svg
Geographic coverage World Fairytale bookmark gold.svgGood article star.svgGood article star.svgGood article star.svgGood article star.svg
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distribution in Africa (wild)
1, base of bole; 2, leaf; 3, leaflet; 4, male inflorescence; 5, female inflorescence; 6, fruit. Redrawn and adapted by Achmad Satiri Nurhaman
base of bole
wood in transverse section
wood in tangential section
wood in radial section

Zanthoxylum heitzii (Aubrév. & Pellegr.) P.G.Waterman

Protologue: Taxon 24: 363 (1975).
Family: Rutaceae


  • Fagara heitzii Aubrév. & Pellegr. (1950),
  • Fagara brieyi Vermoesen ex G.C.C.Gilbert (1958).

Vernacular names

  • Olon tendre (Fr).

Origin and geographic distribution

Zanthoxylum heitzii occurs from southern Cameroon and the Central African Republic to Gabon and Bas-Congo province of DR Congo.


The wood, often traded as ‘olon’ or ‘light olon’, is suitable for light construction, light flooring, joinery, interior trim, moulding, shipbuilding, furniture, cabinet work, toys, novelties, boxes, crates, turnery, veneer, plywood, hardboard and particle board. It is used locally for canoes, drums and beehives. It is sometimes also used as firewood.

Zanthoxylum heitzii is used in traditional medicine. In Cameroon scrapings from the stem bark are applied externally to treat malaria, and in Congo to soothe toothache. In Gabon the bark is applied externally in lotions to treat rheumatism and stiffness, and a maceration of young twigs in lemon juice to treat heart complaints. In Cameroon the bark is used to treat gonorrhoea, abscesses and painful joints and male sexual impotence. In Congo the bark is used as an analgesic. It serves as a fish poison. The tree is sometimes retained by farmers after clearing the forest for agricultural land, to serve as a shade tree for cultivation of crops such as coffee and cocoa.

Production and international trade

The annual production of Zanthoxylum heitzii timber in Gabon in 1994–1995 has been estimated at 5700 m³. The timber of Zanthoxylum heitzii has little importance on the international market and is mostly traded for local use. Few trade statistics are available because the wood of Zanthoxylum gilletii (De Wild.) P.G.Waterman is sometimes sold as ‘olon’ too. Annual olon log exports during the 1960s were 5000–6000 m³ from Equatorial Guinea and 1300–3000 m³/year from Gabon, whereas only very small volumes were exported from Cameroon and Congo. In 1997–1998 Equatorial Guinea exported about 1900 m³/year. According to ATIBT statistics, Gabon exported 310 m³ in 2001, 499 m³ in 2002, 1071 m³ in 2003 and 886 m³ in 2004. Sawnwood exports are insignificant.

The bark is sold on local markets for medicinal purposes, e.g. in Yaoundé (Cameroon), where in 2002 the price was 5–8 XAF (CFA Central Franc) per g.


The heartwood is pale yellow to greenish yellow and indistinctly demarcated from the pale yellow, 1–2 cm wide sapwood. The grain is usually interlocked, sometimes straight, texture fine to moderately coarse. Quartercut surfaces show a slight ribbon-like figure. Freshly cut wood has a slight, pleasant scent. The wood is lustrous.

The wood is medium-weight, with a density of 450–560 kg/m³ at 12% moisture content. It air dries rapidly with slight risk of distortion and checking. The rates of shrinkage are moderate, from green to oven dry 3.7–3.9% radial and 5.7–6.1% tangential. Once dry, it is moderately stable in service.

At 12% moisture content, the modulus of rupture is 72–122 N/mm², modulus of elasticity 10,000–12,400 N/mm², compression parallel to grain 35–51 N/mm², shear 6 N/mm², cleavage 7–12 N/mm and Chalais-Meudon side hardness 1.5–2.9.

The wood saws and works well with ordinary machine and hand tools. Planing may cause some difficulties due to interlocked grain. The moulding, polishing, gluing, painting and varnishing properties are all satisfactory. The screwing and nailing properties are good and the wood holds screws well, but nails are easy to draw. It produces good veneer by slicing and rotary cutting. The wood is not durable and susceptible to fungal, termite, Lyctus and marine borer attacks. The heartwood is resistant to impregnation with preservatives, the sapwood moderately resistant. The sawdust may be irritant; allergic contact dermatitis has been recorded in workers.

The wood contains: cellulose 41–47%, pentosans 10–14%, lignin 30–31% and ash 0.1–0.2%. Solubilities are 1.8–2.4% in hot water, 3.2–5.8% in alcohol-benzene and 11.1–12.7% in 1% NaOH. The wood fibres are 1.17 mm long and 30 μm wide, with a lumen diameter of 21 μm and a cell wall thickness of 8 μm. Good pulps can be obtained from the wood using the kraft process and other chemical pulping processes.

The secondary alkaloid flindersine has been extracted from the heartwood; the bark yielded several lignans, the triterpenes lupeol and lupeone, and the alkaloids skimmianine and 6-methylnitidine.

Adulterations and substitutes

The wood of Zanthoxylum gilletii is often sold as ‘olon’, although it has a higher density and it is harder.


  • Medium-sized to fairly large tree up to 35 m tall; bole branchless for up to 20 m, usually straight and cylindrical, up to 150 cm in diameter, with many woody, prickle-bearing protuberances up to 9 cm long but old trees often lacking these, usually without buttresses but often slightly thickened at base; outer bark grey to greenish grey, smooth to slightly fissured and scaly in old trees, inner bark granular to fibrous, yellowish brown, often mottled with orange; crown large, with ascending, strongly branched branches; branches glabrous, armed with conical prickles.
  • Leaves alternate, clustered at ends of branches, imparipinnately compound with 25–51 leaflets, up to 100 cm long; stipules absent; rachis glabrous, sometimes with small prickles; leaflets nearly opposite, sessile, oblong to oblong-lanceolate, 4–15(–20) cm × 2–5 cm, rounded to slightly cordate and asymmetrical at base, shortly acuminate at apex, margin slightly toothed with rounded teeth, leathery, glabrous, with scattered minute glandular dots, pinnately veined with 10–20 pairs of lateral veins.
  • Inflorescence a terminal or axillary panicle up to 40 cm long, many-flowered with flowers in clusters.
  • Flowers unisexual, regular, 5-merous, small, sessile; sepals united for most of their length, 0.5–1 mm long; petals oblanceolate, c. 2 mm long, white, turning brown; male flowers with 5 stamens, disk conical, thick, ovary rudimentary; female flowers with superior, globose ovary 1–1.5 mm long, stamens rudimentary.
  • Fruit a globose follicle c. 4 mm in diameter, glandular pitted, dehiscent, 1-seeded.
  • Seed globose, c. 2.5 mm in diameter, black and shiny.

Other botanical information

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. Zanthoxylum heitzii is often confused with Zanthoxylum gilletii, which produces a heavier and harder timber and also differs in less numerous and larger leaflets with often entire margins.


Wood-anatomical description (IAWA hardwood codes):

  • Growth rings: 2: growth ring boundaries indistinct or absent.
  • Vessels: 5: wood diffuse-porous; 13: simple perforation plates; 22: intervessel pits alternate; (23: shape of alternate pits polygonal); 25: intervessel pits small (4–7 μm); 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 42: mean tangential diameter of vessel lumina 100–200 μm; 47: 5–20 vessels per square millimetre; (48: 20–40 vessels per square millimetre); 58: gums and other deposits in heartwood vessels.
  • Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 69: fibres thin- to thick-walled.
  • Axial parenchyma: 78: axial parenchyma scanty paratracheal; (79: axial parenchyma vasicentric); (89: axial parenchyma in marginal or in seemingly marginal bands); (91: two cells per parenchyma strand); 92: four (3–4) cells per parenchyma strand.
  • Rays: (97: ray width 1–3 cells); (98: larger rays commonly 4- to 10-seriate); 104: all ray cells procumbent; (106: body ray cells procumbent with one row of upright and/or square marginal cells); 115: 4–12 rays per mm.
  • Secretory elements and cambial variants: (131: intercellular canals of traumatic origin).
  • Mineral inclusions: 136: prismatic crystals present; 142: prismatic crystals in chambered axial parenchyma cells.
(N.P. Mollel, P. Détienne & E.A. Wheeler)

Growth and development

Zanthoxylum heitzii grows rapidly. The seeds are probably dispersed by birds.


Zanthoxylum heitzii occurs in evergreen and semi-deciduous forest, up to 1200 m altitude. It is a pioneer species that is most common in secondary forest. It prefers well-drained soils.

Propagation and planting

Seedlings are light-demanding and natural regeneration may be abundant in larger gaps in the forest. Seeds may germinate 25–30 days after sowing. Seeds that have been soaked in water for longer periods do not germinate.


Mature Zanthoxylum heitzii trees usually occur scattered in the forest. For southern Cameroon average exploitable timber volumes of less than 0.1 m³/ha to 0.8 m³/ha have been recorded, and for Gabon an average timber volume of 0.3 m³/ha.

Diseases and pests

The wood-boring beetle Apate monachus and the hemipterous Lerida punctata have been recorded as pests of Zanthoxylum heitzii in natural forest in Cameroon.


The minimum bole diameter for harvesting is 60 cm in Cameroon and 50 cm in Central African Republic.

Handling after harvest

The wood is susceptible to blue stain and logs should be removed from the forest immediately after felling or be treated with an anti-sapstain chemical. Logs float in water and can be transported by river.

Genetic resources

Zanthoxylum heitzii is valued for its multipurpose timber and there is high demand locally for its bark, which is used in traditional medicine. Although this species is not considered of conservation concern at present, the logging and debarking may make it liable to genetic erosion in the near future. The pressure on the trees because of bark collection can be locally high, as was recorded around the Dja reserve in southern Cameroon.


Zanthoxylum heitzii may have good prospects as a plantation timber tree, but more research is needed on propagation techniques. It seems to be a suitable candidate for sustainable timber exploitation in natural forest because it is able to regenerate in logged-over forest.

The medicinal properties deserve more attention, particularly the analgesic activity. Several of the claimed activities in traditional medicine are comparable to those of Zanthoxylum gilletii, which has been subject to much more pharmacological research, with promising results.

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.
  • CIRAD Forestry Department, 2003. Olon. [Internet] Tropix 5.0. afr/olon.pdf. September 2007.
  • CTFT (Centre Technique Forestier Tropical), 1980. Olon. Bois et Forêts des Tropiques 191: 47–57.
  • de Saint-Aubin, G., 1963. La forêt du Gabon. Publication No 21 du Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 208 pp.
  • Petroff, G., Doat, J. & Tissot, M., 1967. Caractéristiques papetières de quelques essences tropicales de reboisement. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 166 pp.
  • Sallenave, P., 1955. Propriétés physiques et mécaniques des bois tropicaux de l’Union française. Centre Technique Forestier Tropical, Nogent sur Marne, France. 129 pp.
  • Sallenave, P., 1964. Propriétés physiques et mécaniques des bois tropicaux. Premier supplément. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 79 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

  • Adjanohoun, E.J., Ahyi, A.M.R., Aké Assi, L., Baniakina, J., Chibon, P., Cusset, G., Doulou, V., Enzanza, A., Eymé, J., Goudoté, E., Keita, A., Mbemba, C., Mollet, J., Moutsamboté, J.-M., Mpati, J. & Sita, P. (Editors), 1988. Médecine traditionnelle et pharmacopée - Contribution aux études ethnobotaniques et floristiques en République Populaire du Congo. Agence de Coopération Culturelle et Technique, Paris, France. 606 pp.
  • ATIBT (Association Technique Internationale des Bois Tropicaux), 1986. Tropical timber atlas: Part 1 – Africa. ATIBT, Paris, France. 208 pp.
  • ATIBT (Association Technique Internationale des Bois Tropicaux), 2005. Statistics. ATIBT Newsletter 22: 26–47.
  • Betti, J.L., 2001. Vulnérabilité des plantes utilisées comme antipaludiques dans l'arrondissement de Mintom au sud de la réserve de biosphère du Dja (Cameroun). Systematics and Geography of Plants 71: 661-678.
  • Betti, J.L., 2002. Medicinal plants sold in Yaoundé markets, Cameroon. African Study Monographs 23(2): 47–64.
  • Betti, J.L., 2003. Plantes utilisées pour soigner le paludisme dans la réserve du Dja, Cameroun. Revue de Médecines et Pharmacopées Africaines 17: 121–130.
  • Bongui, J.-B., Blanckaert, A., Elomri, A. & Seguin, E., 2005. Constituents of Zanthoxylum heitzii (Rutaceae). Biochemical Systematics and Ecology 33(8): 845–847.
  • Condé-Salazar, D., Guimaraens, D., Romero, V. & Gonzalez, M.A., 1987. Allergic contact dermatitis to Olon wood. Contact Dermatitis 16(4): 231–232.
  • Foahom, B., 2002. Insect pest incidence on timber tree species in natural forest in South Cameroon. Tropenbos-Cameroon Document 12. Tropenbos Cameroon Programme, Kribi, Cameroon. 54 pp.
  • Gassita, J.N., Nze Ekekang, L., De Vecchy, H., Louis, A.M., Koudogbo, B. & Ekomié, R. (Editors), 1982. Les plantes médicinales du Gabon. CENAREST, IPHAMETRA, mission ethnobotanique de l’ACCT au Gabon, 10–31 juillet 1982. 26 pp.
  • Gilbert, G., 1958. Rutaceae. In: Robyns, W., Staner, P., Demaret, F., Germain, R., Gilbert, G., Hauman, L., Homès, M., Jurion, F., Lebrun, J., Vanden Abeele, M. & Boutique, R. (Editors). Flore du Congo belge et du Ruanda-Urundi. Spermatophytes. Volume 7. Institut National pour l’Étude Agronomique du Congo belge, Brussels, Belgium. pp. 69–108.
  • Letouzey, R., 1963. Rutacées. Flore du Cameroun. Volume 1. Muséum National d’Histoire Naturelle, Paris, France. pp. 32–153.
  • Letouzey, R., 1963. Rutacées. Flore du Gabon. Volume 6. Muséum National d’Histoire Naturelle, Paris, France. pp. 3–109.
  • Ngavoura, P., 1990. Fiabilité de la médecine traditionnelle dans le monde moderne - “Contribution du forestier”. Mémoire de fin de cycle, Ecole nationale des eaux et forêts (ENEF), Cap-Estérias, Gabon. 115 pp.
  • Ngouela, S., Tsamo, E. & Connolly, J.D., 1994. Lignans and other constituents of Zanthoxylum heitzii. Phytochemistry 37(3): 867–869.
  • Nkeoua, G. & Boundzanga, G.C., 1999. Données sur les produits forestières non ligneux en République du Congo. FAO, Brazzaville, Congo. 125 pp.
  • Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 pp.
  • Tailfer, Y., 1989. La forêt dense d’Afrique centrale. Identification pratique des principaux arbres. Tome 2. CTA, Wageningen, Pays Bas. pp. 465–1271.
  • Vivien, J. & Faure, J.J., 1985. Arbres des forêts denses d’Afrique Centrale. Agence de Coopération Culturelle et Technique, Paris, France. 565 pp.
  • Wilks, C. & Issembé, Y., 2000. Les arbres de la Guinée Equatoriale: Guide pratique d’identification: région continentale. Projet CUREF, Bata, Guinée Equatoriale. 546 pp.

Sources of illustration

  • Letouzey, R., 1963. Rutacées. Flore du Gabon. Volume 6. Muséum National d’Histoire Naturelle, Paris, France. pp. 3–109.
  • Wilks, C. & Issembé, Y., 2000. Les arbres de la Guinée Equatoriale: Guide pratique d’identification: région continentale. Projet CUREF, Bata, Guinée Equatoriale. 546 pp.


  • R.B. Jiofack Tafokou, Ecologic Museum of Cameroon, P.O. Box 8038, Yaoundé, Cameroon

Correct citation of this article

Jiofack Tafokou, R.B., 2008. Zanthoxylum heitzii (Aubrév. & Pellegr.) P.G.Waterman. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 13 August 2022.