Prota 14: Vegetable oils/Oléagineux
Notizbl. Königl. Bot. Gart. Berlin 1: 100 (1895).
2n = 38
Pycnanthus kombo (Baill.) Warb. (1897).
African nutmeg, boxboard (En). Ilomba, faux muscadier, arbre à suif (Fr). Menebantamo (Po). Mkungu mwitu (Sw).
Origin and geographic distribution
Pycnanthus angolensis is found in the forest zone of tropical Africa, from Senegal and Guinea to Angola, and through DR Congo to Uganda, Tanzania and Zambia.
A yellow to reddish brown fat, called ‘kombo butter’ or ‘Angola tallow’, is extracted from the seed and is important in West and Central Africa for illumination and in soap making. It is not edible. The seeds somewhat resemble those of nutmeg (Myristica fragrans Houtt.) and are burnt as candles. In Central Africa they are used as spice. Traditionally the wood is highly valued as fuel and is used to make split planks, known as ‘calabot’ or ‘caraboard’ in the coastal zone of Cameroon. Because it is easy to work, it is used to make shingles both for roofing and covering the sides of native houses, and planks for doors and window frames. The long straight bole makes it suitable for making canoes. Since the Second World War the wood has become an important timber for plywood corestock, veneer, mouldings, interior trim, interior joinery, furniture components and paper pulp. In agroforestry Pycnanthus angolensis is planted or retained for shade in coffee and cocoa plantations in the humid lowlands of Cameroon, in Uganda often also in banana plantations. Farmers in Cameroon consider it a good indicator of soil fertility. In Uganda it has been planted as an amenity tree.
Throughout its area of distribution, various preparations of the bark, and to a lesser extent other parts of the tree, are used medicinally to treat skin infections, especially of the mouth. Preparations made from the bark are used as a potent purgative, to cleanse the milk of lactating mothers and to treat coughs and chest complaints. In Ghana a decoction of the bark is taken to treat anaemia, in Côte d’Ivoire as a poison antidote and against ascites and leprosy. In Congo the bark is used to treat a number of gynaecological problems, from infertility to gonorrhoea. In Côte d’Ivoire a root macerate mixed with parts of other plants is taken by draught to treat schistosomiasis. In São Tomé the bark is used to treat malaria.
Production and international trade
No information is available on the trade in kombo butter. Trade in the timber ‘ilomba’ began after the Second World War due to an increased demand for plywood and improvements in wood conservation techniques and also as a substitute for okoumé (Aucoumea klaineana Pierre). Trade in ilomba increased spectacularly between 1946 and 1959 from 100 to 5600 boles. Gabon and Cameroon became the first major exporters in 1952/1953, followed by Côte d’Ivoire in 1954 and Congo in 1955. For several years, ilomba was among the most valued timbers in Central Africa. Between 1950 and 1960, the quantity of wood exported from Gabon was 3000 m3, from Cameroon 278,000 m3. Cameroon has enforced a ban on exports of ilomba logs since 1999. Exports of ilomba have fallen drastically. In 2003 the combined exports of veneer, sawnwood and plywood from Cameroon amounted to 72 m3, from Gabon to 816 m3. Exports from the Congo basin dropped to 0.06% of total timber exports or about 3000 m3 in 2003. In 2001 11,000 m3 of ilomba veneer were exported from Côte d’Ivoire at an average price of US$ 240/m3, and 5000 m3 from Ghana at an average price of US$ 351/m3. The export of plywood from Côte d’Ivoire in 2001 amounted to 3000 m3 at an average price of US$ 329/m3, and from Ghana in 2002 to 1000 m3 at an average price of US$ 456/m3.
The seeds of Pycnanthus angolensis are aromatic, but information on volatile constituents is not available. The seeds yield 45–70% of a yellow to reddish brown solid fat known as ‘kombo butter’, which tastes bitter and is suitable for making soap and candles, while the residue is used for manure as it is unsuitable as cattle feed. The melting point of the fat is 51°C. The fatty acid composition of kombo butter is lauric acid 5.5%, myristic acid 61.5%, palmitic acid 3.6%, myristoleic acid 23.6%, oleic acid 5.7%. Crude kombo butter contains about 20% kombic acid (a dihydroxymethylphenyl derivative of hexadecatetraenoic acid) and sargaquinoic acid (a quinone derivative) and several of their derivatives. These terpenoid quinonic acids have promising anti-oxidant properties for pharmacology, cosmetics and the stabilization of plastics. They have also shown hypoglycaemic activity in diabetes patients.
The bark contains dihydroguaiaretic acid, which has shown non-selective toxicity towards several human tumour cell lines. Extracts of the bark also showed the presence of flavonoids (2’-hydroxy-formononetin), tannins and saponin glycosides, which might be responsible for its biological activities. Terpenoid quinones that have shown hypoglycaemic activity in both insulin-dependent and insulin-independent diabetes have been extracted from the bole and leaves.
The heartwood is whitish to pinkish brown, sometimes with yellowish markings and indistinctly demarcted from the sapwood. The grain is generally straight, the texture medium to coarse. The wood has no lustre and when freshly sawn it has an unpleasant odour which disappears on drying.
At 12% moisture the density is 440–570 kg/m3. The wood is rather difficult to dry, it is prone to collapse, end splitting and distortion. Good ventilation is required for air drying. Kiln drying can give good results if done carefully. Shrinkage rates from green to oven dry are 4.6% radial and 8.4% tangential. Drying of beams more than 55 mm thick is very difficult and steaming for 2 days is recommended. At 12% moisture content, the modulus of rupture is 62–72 N/mm2, modulus of elasticity 8300–12000 N/mm2, compression parallel to grain 38–39.5 N/mm2, shear 5.4–8.9 N/mm2, cleavage 13–24 N/mm, Janka side hardness 2700–3400 N.
The wood is easy to saw and plane with normal tools; blunting effects are moderate. It is difficult to polish. Nailing and screwing are easy and holding properties are good. The wood may stain in contact with tools. It peels and slices well to produce good-quality veneer and plywood, although steaming is recommended because of the occasional presence of numerous small hard spots. It glues well with all types of glue. It paints well but is rather absorbent.
The wood is not durable and liable to attack by termites, powder-post beetles, pinhole borers and marine borers, but it is permeable to preservatives.
Evergreen, monoecious or dioecious, medium-sized to large tree up to 25–35(–40) m tall; bole usually straight and cylindrical, branchless for up to 15(–25) m high, up to 120(–150) cm in diameter, usually without buttresses; outer bark greyish brown, with orange-brown exudate; crown small, with branches at right angles to the bole; twigs slender, pendulous, densely rusty hairy. Leaves distichously alternate, simple and entire, without stipules; petiole 1–2 cm long; blade oblong to oblong-lanceolate, 7.5–30(–40) cm × 4.5–11(–16) cm, base cordate, apex acuminate, dark green above, glaucous below, young leaves velvety reddish brown hairy, but glabrescent, pinnately veined with 20–40 pairs of lateral veins. Inflorescence an axillary panicle, often on leafless branches, 10–30 cm long, rusty hairy, with flowers in numerous head-shaped clusters. Flowers unisexual, regular, very small, sessile, with 3-lobed perianth covered with dark brown hairs; male flowers with 2–4 stamens, filaments merged into a column; female flowers with superior, sessile, 1-celled ovary, stigmas 2, sessile. Fruit an ellipsoid to oblong or globose drupe, 3–4.5 cm × 2–4 cm, in bunches, yellowish orange when ripe, fruit wall rather hard and tough, 2–10 mm thick, splitting longitudinally with 2 valves, 1-seeded. Seed ellipsoid, aromatic, 1.5–3 cm × 1–1.5 cm, dark brown, with pink to red aril, laciniate almost to the base. Seedling with epigeal germination, but cotyledons remaining in the testa.
Other botanical information
Pycnanthus comprises 3–4 species, all in Africa. Pycnanthus angolensis is variable, especially in the hairiness of the leaves, the size and shape of the fruits, and reportedly also in the quality of the timber. Two subspecies have been distinguished: subsp. angolensis and subsp. schweinfurthii (Warb.) Verdc., the latter occurring DR Congo and East Africa, but possibly also more to the west, and differing from subsp. angolensis in having larger, often more globose fruits with thicker fruit wall. The wood of Cephalosphaera usambarensis (Warb.) Warb. and several American Virola species closely resembles that of Pycnanthus angolensis. Cephalosphaera usambarensis is restricted to eastern parts of Kenya and Tanzania, where its timber is occasionally used.
Growth and development
Seeds of Pycnanthus angolensis are recalcitrant. The duration of germination is 16–36 days. The cotyledons are pulpy and the first two leaves which appear after two months are simple, opposite or alternate, later leaves alternate. A deep secondary root system develops during the first seven months of growth. In natural stands numerous seedlings appear around the mother tree. In the first year the stem height reaches 20–30 cm and it can reach 50 cm in the second year. In Sierra Leone a mean annual increment in diameter of 1.6–2.4 cm has been observed. Because of the long straight trunk, the volume/trunk ratio is higher than in most other African forest tree species. Pycnanthus angolensis is evergreen, and at any latitude in its range leaf fall and flushing occur simultaneously. The flowering period is long and depends on the location. In Cameroon it flowers in October–May with male and female flowers at separate parts of the same tree, generally also at different times, while it fruits in September–April. Dehiscence takes place on the tree or the whole infructescence falls before dehiscence.
Pycnanthus angolensis occurs in upland and wet evergreen forest and semi-deciduous forest with more than 1600 mm rainfall. It is especially abundant in old fallows and secondary forest as its rate of natural recruitment after disturbance of the forest is high. In southern Africa it occurs in riverine and swamp forest, but in West Africa it does not occur in swamps. In Uganda it also occurs in gallery forest. It is mostly found in small groups or solitary and it regenerates in small to medium-sized gaps in the forest. Its abundance increases with rainfall, the optimum being about 2000 mm/year; above 2600 mm/year numbers decline strongly. It occasionally occurs where rainfall is only 1300 mm or less with 4–5 dry months. Seedlings are very sensitive to drought. Pycnanthus angolensis is a light-demanding tree typical of the dominant forest strata, although it can tolerate slight shade when young. It occurs up to 1200 (–1400) m altitude. Pycnanthus angolensis tolerates light and heavy soils, but is scarce on sandy soils, while other reports indicate that it is often found on poor soils.
Propagation and planting
Pycnanthus angolensis is propagated by seed. There are about 500 seeds per kg. Young broken or cut trees resprout easily, but in a trial vegetative propagation by stem cuttings failed to succeed. Seeds should not be dried, but sown as soon as possible because of their short viability. Germination is easy and with proper care the germination rate of fresh seed can reach 100%. Soaking in cold water for 24 hours hastens germination. In the case of unsorted seeds, the germination rate is about 50%. Seeds can be planted directly in the field or in an open field nursery preferably in polythene bags. It is important to protect the seeds from rodents. A mixture of sand and arable soil (50/50) is a suitable germination substrate. The seedling rapidly grows a large taproot, whose development should be checked timely in the nursery. Cutting the taproot when it is large greatly reduces the plant’s growth rate. It is advisable to transplant seedlings after 1–2 years when 30–50 cm tall, at the beginning of the rainy season. A slight mulching is recommended. In the humid lowlands of Cameroon farmers used to retain or transplant seedlings from the wild when clearing new fields. To improve growth, compost or chemical fertilizer may be applied. In direct sowing in the field, the recommendation is to plant 3–5 seeds per hole and thin to a single plant after germination. Field spacing has been 4 m × 5 m, but recent recommendations are 9 m × 10 m (110 trees/ha).
Protection and retention of natural Pycnanthus angolensis trees has long been done by farmers in the humid lowland forest of West and Central Africa. In plantations the initial thinning should be done when trees are about 7 years old to reduce the density to 300–350 trees/ha; when trees approach the age of 12 years a second thinning should reduce the density to 150–200 trees/ha.
Diseases and pests
Although its leaves are often marred by small holes, no important diseases or pests have been detected in Pycnanthus angolensis in either the natural state or plantations and from a phytosanitary point of view, silviculture of the species is very easy. Nevertheless, some sporadic insect (Monochamus scabiosus, Mallodon downesi, Bryochaeta interrupta) and fungi (Ophiostoma sp., Microthyriella sp.) attacks have been reported in Côte d’Ivoire, Cameroon and Gabon.
In good plantations in the evergreen forest zone the exploitable diameter of 50 cm is reached when trees are 30 years old, and a diameter of 60 cm at 45 years.
Little information on seed yield is available; an average tree may produce 60–100 seeds annually. In well growing plantations the annual increment at 15 years of age is 15 m3/ha/year, at 30 years it can be 10 m3/ha/year.
Handling after harvest
Logs should be treated with preservatives and be converted soon after felling to avoid discoloration by fungi and damage by insects. Logs can be floated and be transported by river.
Because of its wide distribution and occurrence in secondary forest, there is little risk of genetic erosion. No genetic conservation programme is known to exist.
Pycnanthus angolensis is one of the most important agroforestry tree species of the humid lowland forest of West and Central Africa identified by the World Agroforestry Centre (ICRAF) for a domestication programme.
Pycnanthus angolensis is an important medicinal plant in the humid forest region. It is traditionally protected by farmers during forest clearing. Large amounts of timber have been exported, but recently volumes have dropped markedly. The export of the wood as veneer and plywood has been most important in recent years. New opportunities for exploiting the oil and medicinal properties should be investigated. However, as a fairly fast-growing species that is not very liable to diseases and pests, Pycnanthus angolensis seems to have good prospects for timber plantations and for sustainably managed natural production forest.
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Correct citation of this article:
Mapongmetsem, P.-M., 2007. Pycnanthus angolensis (Welw.) Warb. In: van der Vossen, H.A.M. & Mkamilo, G.S. (Editors). PROTA 14: Vegetable oils/Oléagineux. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, base of bole; 2, leafy twig; 3, inflorescence; 4, fruit; 5, seed.
Redrawn and adapted by Iskak Syamsudin
wood in transversal section
wood in radial section
wood in tangential section
cross section of a fruit