Prota 7(1): Timbers/Bois d’œuvre 1
Bot. Jahrb. Syst. 18: 171 (1893).
Verbenaceae (APG: Lamiaceae)
2n = 96
Vitex keniensis Turrill (1915).
Meru oak, Kenya oak (En). Mfuu, mfudu (Sw).
Origin and geographic distribution
Vitex fischeri occurs wild from DR Congo and southern Sudan east to Kenya and south to Angola and Zambia. It has been planted in the highlands of Kenya, Uganda and Tanzania, and in Cameroon.
The wood is used for furniture, coffin boards, panelling and veneer. In Kenya it is in high demand for furniture, and is also popular for making tool handles and oxen yokes. The wood is suitable for light construction, flooring, joinery, interior trim, shipbuilding, vehicle bodies, toys, novelties, boxes, crates, carving, turnery, draining boards, hardboard, particle board and pulpwood. It is used as firewood and for charcoal production.
The blackish pulp of the fruits is edible and eaten raw. It has been recorded that the honey produced by bees visiting Vitex fischeri flowers is of superior quality and fetches high prices in the market. Vitex fischeri is planted as a shade tree for crops such as coffee and yam, and may be retained in maize and cassava fields. It is grown as an ornamental and windbreak. It produces a useful mulch and serves as a soil improver.
Production and international trade
Meru oak timber appears to be traded only in local markets and in small amounts. In Kenya, where the wood is prized and in high demand, the annual volume traded has been estimated at about 400 m³. Fruits are traded on local markets on a small scale.
The heartwood is pale grey-brown and indistinctly demarcated from the sapwood, with heartwood of older trees often dark stained and decorative. The grain is straight or wavy, texture coarse. The wood resembles teak, and often yellows after some time in service. Logs are often rotten in the core. The wood is medium-weight, with a density of 430–570 kg/m³ at 12% moisture content. It air dries easily, with little deformation; the rates of shrinkage are moderate. The wood is easy to saw and work with hand and machine tools. It planes to a smooth surface, but a filler is needed for polishing and varnishing. It nails well. The gluing properties are good, and veneer of excellent quality can be produced. Assessments of the durability of the wood range from non-durable to durable. The heartwood is moderately resistant to impregnation with preservatives, the sapwood is permeable.
Deciduous small to fairly large tree up to 35 m tall; bole branchless for up to 18 m, up to 180(–230) cm in diameter; bark very thin, bark surface grey to dark brown, smooth to rough and slightly fissured, inner bark creamy yellow to pale brown; crown rounded; young branches densely velvety hairy. Leaves opposite, digitately compound with 5 leaflets; stipules absent; petiole 6.5–17 cm long; petiolules up to 4 cm long; leaflets obovate to elliptical, 5–19 cm × 3–10 cm, rounded to acuminate at apex, entire, leathery, densely hairy and glandular below. Inflorescence an axillary cyme up to 12 cm long and 24 cm wide, densely hairy; peduncle 6–14 cm long; bracts up to 2 cm long. Flowers bisexual, zygomorphic, 5-merous; pedicel 1–4(–12) mm long; calyx campanulate, 2.5–4 mm long, with minute teeth, enlarging in fruit; corolla white, often tinged blue, tube 3–6 mm long, limb 2-lipped, 3–5 mm long, upper lip 2-fid, lower 3-fid; stamens 4, inserted in the corolla tube, 2 long and 2 short; ovary superior, globose, 4-celled, style c. 6 mm long. Fruit an obovoid to oblong-globose drupe 1–2.5 cm long, blackish with whitish or greenish spots, fleshy, with woody, 4-celled stone, up to 4-seeded. Seeds without endosperm.
Other botanical information
Vitex comprises about 150 species and is pantropical with a few species in temperate regions. Approximately 60 species occur in tropical Africa.
Vitex keniensis Turrill is often considered to represent a separate species, distinguished from Vitex fischeri by its larger tree size, more shaggy indumentum, more lax inflorescence, more distinctly toothed calyx and larger fruit. It occurs mainly in montane rainforest, whereas Vitex fischeri is found in wooded grassland and thickets. However, a biosystematic study of Vitex keniensis and Vitex fischeri populations revealed no reason for taxonomic separation. It was also demonstrated that different populations are not reproductively isolated.
Vitex congolensis De Wild. & T.Durand is a small to medium-sized tree up to 30 m tall, known from the Central African Republic and DR Congo. Its wood is suitable for similar purposes as that of Vitex fischeri; its density is slightly higher (about 600 kg/m³ at 12% moisture content) and it is somewhat more durable.
Wood-anatomical description (IAWA hardwood codes):
Growth rings: 1: growth ring boundaries distinct. Vessels: (4: wood semi-ring-porous); (5: wood diffuse-porous); 13: simple perforation plates; 22: intervessel pits alternate; 26: intervessel pits medium (7–10 μm); (30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell); 31: vessel-ray pits with much reduced borders to apparently simple: pits rounded or angular; 32: vessel-ray pits with much reduced borders to apparently simple: pits horizontal (scalariform, gash-like) to vertical (palisade); (33: vessel-ray pits of two distinct sizes or types in the same ray cell); 43: mean tangential diameter of vessel lumina ≥ 200 μm; 46: ≤ 5 vessels per square millimetre. Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 65: septate fibres present; 69: fibres thin- to thick-walled. Axial parenchyma: 78: axial parenchyma scanty paratracheal; (79: axial parenchyma vasicentric); (80: axial parenchyma aliform); (81: axial parenchyma lozenge-aliform); 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); 106: body ray cells procumbent with one row of upright and/or square marginal cells; (110: sheath cells present); 114: ≤ 4 rays per mm; 115: 4–12 rays per mm.
(M. Thiam, P. Baas & P. Détienne)
Growth and development
Seedlings have simple leaves in the early stages and start to produce compound leaves after about 3 months. Vitex fischeri trees grow moderately fast. In a plantation in Kenya, trees were on average 35 m tall 56 years after planting. Maximum mean annual volume increment was reached 25–30 years after planting, and a marked decline in volume increment was recorded when trees were more than 35 years old. Trees of 50 years old may reach a bole diameter of 60 cm.
In Kenya trees flower from December to March, before the long rainy season starts in April. The flowers are pollinated by insects such as bees. However, fruits can be produced by both self- and cross-pollination. In Kenya ripe fruits can be found from June to November, and fruit maturity coincides with leaf fall. In Tanzania ripe fruits are available from April to August. The seeds are dispersed by animals such as monkeys and hornbills that eat the fruits.
Vitex fischeri occurs in evergreen forest, open woodland, wooded grassland and thickets, up to 2100 m altitude. In Kenya the mean annual temperature in the distribution area of Vitex fischeri is 15–23°C, and mean annual rainfall 1200–2000 mm. On the slopes of Mount Kenya it prefers deep sandy loam soils, but it is elsewhere locally common in thickets on granite rocks and in wooded grassland on termite mounds.
Propagation and planting
In montane rainforest in central Kenya, natural regeneration of Vitex fischeri occurs particularly in forest gaps, and is poor in closed forest. Seeds for propagation can best be collected when most fruits are still green while about 20% have turned brown. All fruits collected should have grown to the final size. After collection, fruits are packed in gunny-bags. The pulp should be removed within a few days, after which the stones are dried in the shade up to a minimum moisture content of 8.5%, and can be stored subsequently. The germination rate of fresh seeds is 40–50% after 9 weeks. Fruit stones are usually used for propagation; one kg contains 2500–3000 stones. Several seedlings may germinate from one stone because it may contain 1–4 seeds. Soaking in cold water for 24 hours improves germination. When the fruit pulp has been removed and the stones dried in the shade, they can be stored for considerable time (at least one year) if they are kept dry and cool. Although seedlings are light demanders, they tolerate shade. In the nursery they still showed good growth at an irradiance level of 19% of full sun, but higher levels of light enhanced growth. Wildlings are sometimes also collected for planting.
The first timber plantation was established in the early 1950s on the slopes of Mount Kenya. In 1973 about 620 ha of plantations were recorded. The rotation for trees planted on farms for timber production is recorded to be 35 years, but in commercial timber plantations with a stand density of 200 trees per ha, a cycle of 45–60 years seems more appropriate. Pruning is recommended to obtain a straight and clear bole. Trees tolerate coppicing. They can also be lopped and pollarded, thus providing farmers with fuelwood while allowing the bole to reach marketable size.
Diseases and pests
Seedlings in nurseries are susceptible to damping-off caused by fungal attacks. Parasitic plants of the genus Cuscuta can cause serious losses in nursery seedlings. The fungus Armillaria mellea often attacks the tree in plantations resulting in a black resin on the stems and in decay accelerated by Trichoderma sp. However, this disease is usually not a serious threat and can be controlled by uprooting affected trees at first thinning.
In general Vitex fischeri is widespread and not uncommon in many regions in its distribution area. However, the populations in montane rainforest in central Kenya, where the boles are often straight and reach large dimensions and are thus of high value in the timber trade, have been overexploited. These populations, referred to as Vitex keniensis, are classified as vulnerable in the 2006 IUCN Red list. In several other habitats and regions, Vitex fischeri is also threatened because of forest clearing for human settlement and agriculture, e.g. near Lake Victoria and at the foot of Mount Elgon.
KEFRI and the Plant Conservation Programme in Kenya maintain a living collection of Vitex fischeri, as well as seed stocks. Research showed that the bulk of genetic variation in natural populations in Kenya is within populations (96.5%), and therefore sampling from any of these populations would capture a sufficiently large genepool of the species for breeding and conservation.
Vitex fischeri is already planted in agroforestry systems, but it has substantial potential for larger-scale planting, not only for timber production, but also as a source of firewood, edible fruits and honey, and as a useful auxiliary tree. Efforts to promote planting and conservation of Vitex fischeri are hampered by lack of information on its biological and ecological characteristics. More research is needed on the variation in wood properties between different populations, and on the role of the ecological conditions on wood properties, the results of which might be used in breeding programmes.
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Sources of illustration
• Dale, I.R. & Greenway, P.J., 1961. Kenya trees and shrubs. Buchanan’s Kenya Estates Limited, Nairobi, Kenya. 654 pp.
Correct citation of this article:
Thijssen, H.J.C., 2008. Vitex fischeri Gürke. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, tree habit; 2, part of flowering branch; 3, flower; 4, infructescence.
Redrawn and adapted by Iskak Syamsudin
wood in transverse section
wood in tangential section
wood in radial section