Brachylaena huillensis (PROTA)
|Geographic coverage Africa|
|Geographic coverage World|
|Carbohydrate / starch|
|Essential oil / exudate|
Brachylaena huillensis O.Hoffm.
- Protologue: Bot. Jahrb. Syst. 32: 149 (1902).
- Family: Asteraceae (Compositae)
- Brachylaena hutchinsii Hutch. (1910).
- Lowveld silver oak, silver oak (En).
- Muhuhu, mkarambati, mvumo (Sw).
Origin and geographic distribution
Brachylaena huillensis occurs from Kenya and Uganda south to north-eastern South Africa, and also in Angola.
The wood, commonly traded as ‘muhuhu’ is mainly used for construction, first-grade flooring, joinery, interior trim, furniture, fence posts, toys, novelties, boxes, crates, tool handles, carving and turnery. In Kenya it is one of the most highly favoured woods for carving, in Tanzania also for fence posts. In South Africa it is popular for main posts of local houses. It is also suitable for bridges, hydraulic works, poles, piles, cabinet work and railway sleepers. It is considered an excellent firewood and is used for charcoal production.
In traditional medicine, root decoctions are used to treat schistosomiasis and leaves to treat diabetes. The aromatic oil extracted from the wood is used for perfumery. In Kenya Brachylaena huillensis is planted as ornamental and boundary tree around dwellings. Male flowering trees are a source of pollen for honey bees.
Production and international trade
Brachylaena huillensis wood has been exported as short logs from Kenya to India for use as a substitute of sandalwood (from Santalum album L.). It is currently traded locally and across borders, especially between Kenya and Tanzania, but the trade is mainly illegal and consists of billets for wood carving. The annual volume of wood consumed in Kenya by the carving industry has been estimated in 2001 at 15,000 m³, of which 57% was contributed by Brachylaena huillensis.
The heartwood is greyish yellow to yellowish brown or greenish brown and distinctly demarcated from the 1.5–4 cm wide, creamy white to greyish white sapwood. The grain is straight to interlocked, texture fine and even. The wood has a persistent spicy odour. Quarter-sawn surfaces have a faint stripe figure.
The wood is heavy with a density of 830–990 kg/m³ at 12% moisture content. In small dimensions it air dries rapidly and well with little or no degrade, although serious checking may occur in boards of over 25 mm thick; mild drying conditions are recommended for thick material. The rates of shrinkage are low to moderate, from green to oven dry about 3.3% radial and 4.7% tangential. Once dry, the wood is very stable in service.
At 12% moisture content, the modulus of rupture is 100–112 N/mm², modulus of elasticity 10,100 N/mm², compression parallel to grain 51–70 N/mm², shear 23 N/mm², cleavage 18 N/mm, Janka side hardness 9740–11,100 N and Janka end hardness 12,900 N.
The wood is difficult to saw and work with hand tools, but works well with machines. It has moderate blunting effect on cutting edges and saw teeth, but teeth tend to collect gum. A 15° cutting angle is recommended in planing operations. The wood sands easily and takes a fine polish and smooth surface. Boring and mortising properties are less favourable with a tendency of splitting at exits. The wood moulds and turns well, but is difficult to nail and glue. It is not suitable for veneer and plywood. The steam bending properties are moderate to poor. The wood is very durable with an expected outdoor service life of 25–50 years. It is highly resistant to all insect and fungal attacks and is also durable in sea water, where it is resistant to marine borers. The heartwood is extremely resistant to impregnation by preservatives.
Fresh leaves have 5% essential oil that can be isolated by hydrodistillation. The main components of the oil are the sesquiterpene hydrocarbons caryophyllene (19%), β-cubebene (15.5%), cis-calamenene (10.5%) and α-copaene (9%). The oil exhibited antibacterial activity against Proteus mirabilis comparable that of the widely used antibiotic gentamicin. It has also shown some activity against Bacillus cereus, Staphylococcus aureus, Staphylococcus epidermidis, Micrococcus luteus and Enterococcus faecalis.
The methanol extract from the bark yielded ketoaldehyde sesquiterpenes and corresponding ketoalcohols. The ketoaldehyde sesquiterpenes showed some antibacterial activity against gram-positive bacteria, particularly Streptococcus mutans and Brevibacterium ammoniagenes.
Adulterations and substitutes
The wood of Androstachys johnsonii Prain is quite similar to that of Brachylaena huillensis and used for similar purposes. The wood of Brachylaena huillensis has often been traded to India as an inferior substitute of sandalwood for use in funeral ceremonies.
- Evergreen or deciduous, dioecious shrub or small to medium-sized tree up to 30(–40) m tall; bole usually slender, often low-branching, up to 60(–80) cm in diameter, often curved, fluted, eventually developing thin buttresses; bark surface rough, longitudinally fissured, flaking in long narrow strips, grey, inner bark fibrous, pale brown, rapidly becoming dirty grey upon exposure; crown narrow, with steeply ascending branches; young twigs densely whitish short-hairy.
- Leaves arranged spirally, crowded at the ends of twigs, simple; stipules absent; petiole 0.5–1(–1.5) cm long; blade oblanceolate to obovate or elliptical, 3–12(–15) cm × 1–3(–5.5) cm, usually cuneate at base, short-acuminate at apex, margins usually entire, sometimes remotely toothed, leathery, glabrous and shiny green above, densely short-hairy and silvery whitish or greyish below, pinnately veined with up to 16 pairs of lateral veins.
- Inflorescence a small, cylindrical head 2–6 mm long, 3–9-flowered, clustered on short side-branches or in axillary panicles; involucral bracts in several series, densely whitish short-hairy.
- Florets unisexual, 5-merous; corolla white, with cylindrical tube and slightly unequal, recurved lobes; male florets with exserted stamens having fused anthers, and rudimentary ovary; female flowers with inferior ovary and long slender style 2-branched at apex.
- Fruit a cylindrical achene 3–4 mm long, 5–8-ribbed, densely hairy and glandular, crowned by pappus of numerous pale brown bristles 4–6.5 mm long, 1-seeded.
Other botanical information
Brachylaena comprises about 11 species and occurs in eastern and southern mainland Africa (6 species) and in Madagascar (5 species).
The distribution area of Brachylaena discolor DC. (synonym: Brachylaena rotundata S.Moore) partly overlaps with that of Brachylaena huillensis. It is a shrub or small to medium-sized tree up to 20(–30) m tall with bole up to 45(–90) cm in diameter found in evergreen forest, deciduous bushland, secondary vegetation and dune forest in Botswana, Zimbabwe, Mozambique, South Africa and Swaziland, up to 1800 m altitude. Its wood is locally used for boat building, fence posts, axles and spokes of wheels, handles, bows and carving. Branches are used as fire-sticks. In traditional medicine leaf infusions are administered to treat diabetes and kidney complaints, as emetic and tonic, and against intestinal parasites. A root maceration is applied as an enema to treat gastric bleeding, whereas root infusions and decoctions are applied to treat syphilis, dysmenorrhoea and abdominal pain. Brachylaena discolor has been used for afforestation of dunes and is a decorative ornamental tree and hedge plant, and is additionally popular with bee keepers.
Wood-anatomical description (IAWA hardwood codes):
- Growth rings: 1: growth ring boundaries distinct.
- Vessels: 5: wood diffuse-porous; 7: vessels in diagonal and/or radial pattern; 10: vessels in radial multiples of 4 or more common; 13: simple perforation plates; 22: intervessel pits alternate; (23: shape of alternate pits polygonal); 24: intervessel pits minute (≤ 4 μm); 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 40: mean tangential diameter of vessel lumina ≤ 50 μm; 50: ≥ 100 vessels per square milllimetre; 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); 70: fibres very thick-walled.
- Axial parenchyma: 76: axial parenchyma diffuse; 78: axial parenchyma scanty paratracheal; 91: two cells per parenchyma strand; 92: four (3–4) cells per parenchyma strand.
- Rays: (96: rays exclusively uniseriate); 97: ray width 1–3 cells; 104: all ray cells procumbent; (106: body ray cells procumbent with one row of upright and/or square marginal cells); 116: ≥ 12 rays per mm.
- Storied structure: 118: all rays storied; 120: axial parenchyma and/or vessel elements storied.
Growth and development
The growth of Brachylaena huillensis is slow, with an average diameter growth rate of 0.5–2.3 mm/year in natural stands in dry areas in Tanzania. In plantations in a region with an annual rainfall of 760 mm, trees reached up to 4.5 m tall with a bole diameter of 4.6 cm 5.5 years after planting, but in a region with an annual rainfall of 1780 mm they reached up to 9 m tall with a bole diameter of 8.5 cm 5 years after planting, with a very straight bole.
Usually the tree flowers and produces seeds profusely twice every year. Flowering heads appear between March and June and between October and January. Flowers open at the beginning of the rainy season. Bees and flies visit the male flower heads for the pollen and may serve as pollinators when they visit subsequently trees with female flower heads, which do not produce pollen but are visually similar. Fruit development after flowering is very rapid. The fruits with their pappus hairs are dispersed by wind. However, a study in Kenya showed that 98% of the fruits fell within 14 m of the mother tree and that nearly all seedlings are found within that distance.
Brachylaena huillensis can be found in diverse forest types, in dry evergreen and semi-deciduous forest, but also in scrub vegetation, from sea-level up to 2000 m altitude. The tree grows in a wide range of rainfall zones, with an average annual rainfall of 500–1600 mm. The mean annual temperature in the area of distribution ranges from 15°C to 32°C. Brachylaena huillensis prefers light, free-draining sandy soils, well-developed volcanic clayey loams, and red soils of coastal belts, but it is also found on rocky soils and stony hill sides, where it reaches only small dimensions.
Propagation and planting
Brachylaena huillensis is normally propagated by seed. However, the fruits are difficult to collect because of their relatively small size. There are 330,000–500,000 seeds per kg. Mixing of fruits with sand is recommended before sowing to prevent spreading by wind. The germination rate is usually low, although under laboratory conditions 25–50% of the seeds may germinate. In natural forest germination rates are not more than 6%. Up to 80% of the massive fruit produce is subject to predispersal predation by insects and soil organisms may further decrease viability of the seeds on the ground. Complete loss of viability of seed occurs within 4 months in the forest. The fruits do not store well; viability is lost within 6 months in open storage at room temperature, although under laboratory conditions seed remained viable for over a year.
In a test seedlings remained healthy but showed poor growth under conditions of 2–14% of full sunlight, and remained healthy and showed good growth under conditions of 45% of full sunlight. Under full light seedlings grew fast in the nursery but developed a poor stem form. Therefore, partial shading in the nursery is recommended.
In Tanzania stump planting was not successful, but plants raised in polythene tubes were planted into the field when 12 months old and 30–40 cm tall with a survival rate of 80% after 2 years.
In general, larger trees of Brachylaena huillensis occur scattered and in low densities in the forest because of heavy exploitation. In Dindili catchment forest reserve in Tanzania, the average density of Brachylaena huillensis was 15 stems of more than 4 cm diameter per ha, and the average density of seedlings 400 per ha.
Information regarding plantation development and silvicultural management is limited, as only small trial plantations have been established in Kenya and Tanzania. However, the trees are easy to raise in plantations and growth seems to be fair on good soils. They have self-pruning ability. Re-sprouting of coppice stumps is reported to be poor.
Diseases and pests
Various insects feed on fruits, which is a major cause of the low viability of seeds.
Handling after harvest
Logs do not float in water. The bole of old trees is often hollow. In storage logs are not subject to any degrade.
The population of Brachylaena huillensis has rapidly declined due to selective logging for its valuable timber for the local wood carving industries in Kenya and Tanzania. In 2001 most wood consumed by the wood carving industry in Kenya was in the log diameter class of 10–16 cm, indicating resource scarcity with a shift towards younger trees. In 2002 it was estimated that with the current illegal and unsustainable extraction of Brachylaena huillensis wood in Kenya the resource would be depleted in 2–3 decades. In Tanzania Brachylaena huillensis is still locally common, but the high demand from Kenya has led to massive illegal importation of logs from Tanzania. In southern Africa it is one of the favoured woods for poles for hut and house construction and this may have serious local effects on populations of the species, the more so as young trees can already serve this purpose. In South Africa populations partly occur in protected areas and are therefore more secure. Brachylaena huillensis is included in the IUCN Red list of threatened species, where it is still considered to be at lower risk although near threatened. However, updating of the status of the species is needed.
Brachylaena huillensis is a highly valued source of wood for the local carving industry and for local construction, but the slow growth is a serious limitation for sustainable exploitation of natural populations. It has been estimated that under natural conditions a tree will take at least 100 years to reach a bole diameter of 40 cm. Very little information is available on planted trees, but research is recommended because growth rates seem to be more acceptable under favourable conditions and with appropriate management.
The results of phytochemical investigations on the essential oil should stimulate further research as a basis for drug development and for use in the perfume industry.
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Correct citation of this article
Nyemb, Nyunaï, 2010. Brachylaena huillensis O.Hoffm. [Internet] Record from PROTA4U. Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.
Accessed 28 March 2023.
- See the Prota4U database.