Acacia galpinii (PROTA)

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Plant Resources of Tropical Africa
Introduction
List of species


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distribution in Africa (wild)
1, tree habit; 2, leafy twig; 3, flowering twig; 4, fruit. Redrawn and adapted by Achmad Satiri Nurhaman
tree habit (EcoPort)
bark (EcoPort)
leaves and flowers (B. Wursten)
inflorescences (EcoPort)
inflorescence with flower buds (EcoPort)
fruits (EcoPort)

Acacia galpinii Burtt Davy


Protologue: Bull. Misc. Inform. Kew 1922(10): 326 (1922).
Family: Mimosaceae (Leguminosae - Mimosoideae)
Chromosome number: 2n = 40

Vernacular names

  • Monkey thorn (En).

Origin and geographic distribution

Acacia galpinii occurs in Tanzania, Malawi, Zambia, Botswana, Zimbabwe, Mozambique and northern South Africa. Experimental plantations exist in Madagascar.

Uses

The wood is used for interior and exterior joinery, fences, wagons, railway sleepers and as mining timber. It is suitable for flooring, shipbuilding, sporting goods and implements. Acacia galpinii is occasionally planted as ornamental or roadside tree.

Production and international trade

The wood is only used locally and not traded on the international market.

Properties

The heartwood is reddish brown to dark brown and distinctly demarcated from the creamy sapwood. The grain is often irregular, texture moderately coarse. The density of the wood is about 800 kg/m³ at 11% moisture content. Shrinkage during drying is medium. At 11% moisture content, the modulus of rupture is 112 N/mm², modulus of elasticity 13,140 N/mm², compression parallel to grain 61 N/mm², shear 15.9 N/mm², Janka side hardness 9070 N and Janka end hardness 10,100 N. Although the wood is tough and resilient, it works well with sharp tools, but sawing requires considerable strength. A good finish can be obtained with waxes and oil. The wood has good natural durability, being fairly resistant to decay and termite attack, but the sapwood is susceptible to attack by Lyctus borers and blue stain fungi.

The wood is almost free of tannins, but contains a range of flavonoids and melacacidin. A number of proteracacinidins (proanthocyanidins) have been isolated from the heartwood.

Description

  • Small to fairly large tree up to 30 m tall; bole usually straight, up to 60(–150) cm in diameter; bark rough, flaking or longitudinally furrowed, greyish to greyish brown, often with yellowish tinge; crown spreading, rounded; branchlets glabrous to shortly hairy, with pairs of hooked, blackish prickles up to 1 cm long just below the nodes.
  • Leaves alternate, bipinnately compound, with 6–14 pairs of pinnae; stipules linear-oblong, c. 2 mm long, caducous; petiole c. 3 cm long, with small gland in upper half, rachis 6–11 cm long, with glands between top pairs of pinnae; leaflets in (8–)13–35(–45) pairs per pinna, narrowly oblong to linear-oblong, (2–)4–11 (–15) mm × (0.5–)1–3(–4) mm, oblique at base, apex obtuse to acute, glabrous but often with some hairs at margins.
  • Inflorescence an axillary spike 4–11 cm long, often in fascicles on short lateral leafless shoots; peduncle 0.5–1.5 cm long.
  • Flowers bisexual, regular, 5-merous, small, fragrant, sessile; calyx cup-shaped, 0.5–1.5 mm long, red to purple; corolla c. 2 mm long, with short lobes, red to purple; stamens numerous, free, up to 5 mm long, creamy yellow; ovary superior, stalked, style slender, up to 5 mm long.
  • Fruit an oblong to linear pod 11–28 cm × 2.5–3.5 cm, straight, glabrous, reddish to purplish brown, longitudinally dehiscent, up to 12-seeded.
  • Seeds flattened ovoid, 12–15 mm × 10–12 mm.

Other botanical information

Acacia is a large pantropical genus, comprising more than 1300 species; most of them distributed in Australia (more than 900), more than 200 in America, and about 130 in Africa. Acacia galpinii belongs to subgenus Aculeiferum, which includes all African Acacia species with non-spinescent stipules and hooked prickles.

Acacia polyacantha

Acacia galpinii is often confused with Acacia polyacantha Willd., but the latter has a larger gland near the base of the petiole, and a larger number of pinnae per leaf. The wood of Acacia polyacantha is used for similar purposes as the wood of Acacia galpinii, but its gum is more important.

Acacia burkei

The wood of Acacia burkei Benth. (black monkey thorn) has also been used for furniture and wagons, but it is heavier and darker and supplies are limited. This species occurs in about the same region as Acacia galpinii, and may reach 27 m tall; it has fewer pinnae and leaflets per leaf.

Acacia goetzei

The chocolate-brown heartwood of Acacia goetzei Harms is used for construction, heavy joinery and furniture; it is very hard, heavy and durable. Acacia goetzei occurs further north than Acacia galpinii, to Ethiopia, and has fewer pinnae pairs and thicker pod valves.

Anatomy

Wood-anatomical description (IAWA hardwood codes):

  • Growth rings: (1: growth ring boundaries distinct); (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); 26: intervessel pits medium (7–10 µm); 29: vestured pits; 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; (41: mean tangential diameter of vessel lumina 50–100 µm); 42: mean tangential diameter of vessel lumina 100–200 µm; 46: = 5 vessels per square millimetre; (47: 5–20 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; 70: fibres very thick-walled.
  • Axial parenchyma: 79: axial parenchyma vasicentric; 80: axial parenchyma aliform; 81: axial parenchyma lozenge-aliform; 83: axial parenchyma confluent; (89: axial parenchyma in marginal or in seemingly marginal bands); (90: fusiform parenchyma cells); 91: two cells per parenchyma strand; 92: four (3–4) cells per parenchyma strand.
  • Rays: 98: larger rays commonly 4- to 10-seriate; 104: all ray cells procumbent; 115: 4–12 rays per mm.
  • Mineral inclusions: 136: prismatic crystals present; 142: prismatic crystals in chambered axial parenchyma cells.
(M. Thiam, P. Détienne & E.A. Wheeler)

Growth and development

Young Acacia galpinii trees grow fast. In Zimbabwe the average heights of planted trees under conditions of frequent drought were 3 m after 3 years and 5 m after 9 years, and average bole diameters 10 cm after 3 years and 16 cm after 9 years. In 2 locations in Madagascar, at 770 m altitude with a mean temperature of 21°C and an annual rainfall of 1150 mm, and at 100 m altitude with a mean temperature of 27°C and an annual rainfall of 1600 mm, 35-years-old planted Acacia galpinii trees had a mean bole diameter of 26 cm and 32 cm, respectively (maximum 74 cm), and a mean height of 25 m (maximum 30 m). The tree is comparatively long-lived. It is deciduous, losing its leaves in the cool season. In the hot season it provides dappled shade allowing some sunlight to penetrate. Trees may flower when leafless, but they usually flower while leaves are developing in September–January. Insects such as bees and wasps visit the flowers. The fruits take about 6 months to ripen.

Acacia galpinii nodulates well with indigenous Rhizobium and Bradyrhizobium bacteria.

Ecology

Acacia galpinii typically occurs in riverine woodland, but it can also be found scattered on termite mounts and in open woodland, at 350–1500 m altitude. It is most common on loamy or clayey soils. Older trees are frost-tolerant.

Propagation and planting

Seeds germinate easily, but soaking the seeds in hot water for one night prior to sowing is advantageous. Seeds can be sown in seedling trays filled with river sand and covered with vermiculite. Seedlings generally show good survival, even under regular drought conditions. In experimental plantings in Zimbabwe seedlings showed a survival rate of 86%.

Management

Under natural conditions, regeneration of Acacia galpinii is usually good. In suitable habitats, it even acts as a pioneer. Young Acacia galpinii trees coppice well.

Yield

Being a larger sized Acacia, Acacia galpinii gives a comparatively high yield of workable wood. Individual trees may yield up to 2.5 m³ of bole wood.

Handling after harvest

Large planks can be sawn from the bole and sometimes sawlogs can also be obtained from the larger branches of the crown.

Genetic resources

Although Acacia galpinii is fairly widespread, it is not very common in most regions. However, it is not under threat of genetic erosion.

Prospects

Acacia galpinii is an interesting timber tree of drier regions. It nodulates well and grows fast, and so it would be a potential candidate for testing for afforestation in dry regions, and it is an excellent shade tree for lawns in parks and large gardens.

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.
  • Brenan, J.P.M., 1970. Leguminosae (Mimosoideae). In: Brenan, J.P.M. (Editor). Flora Zambesiaca. Volume 3, part 1. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 153 pp.
  • Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
  • Mlambo, D., Nyathi, P. & Mlilo, P., 2004. Early growth and survival of Acacia galpinii after planting in a semi-arid environment in Zimbabwe. Southern African Forestry Journal 202: 61 66.
  • Mutshinyalo, T., 2003. Acacia galpinii Burtt Davy. [Internet]South African National Biodiversity Institute. http://www.plantzafrica.com/ plantab/acaciagalpin.htm. December 2007.
  • Ross, J.H., 1975. Fabaceae, subfamily Mimosoideae. In: Ross, J.H. (Editor). Flora of southern Africa. Volume 16, part 1. Botanical Research Institute, Department of Agricultural Technical Services, Pretoria, South Africa. 159 pp.
  • Timberlake, J., Fagg, C. & Barnes, R., 1999. Field guide to the Acacias of Zimbabwe. CBC Publishing, Harare, Zimbabwe. 160 pp.

Other references

  • Bennie, L., Coetzee, J., Malan, E. & Ferreira, D., 2002. Structure and stereochemistry of dimeric proteracacinidins possessing the rare C-4(C) leads to C-5(D) interflavanyl linkage. Phytochemistry 59(6): 673–678.
  • de Winter, B., de Winter, M. & Killick, D.J.B., 1966. Sixty-six Transvaal trees. Botanical Research Institute, Pretoria, South Africa. 175 pp.
  • Malan, E. & Roux, D.G., 1975. Flavonoids and tannins of Acacia species. Phytochemistry 14(8): 1835–1841.
  • 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.
  • Sutter, E. & Rakotonoely, J., 1989. Projet inventaire des resources ligneuses. Rapport d’activités. FO.FI.FA – D.R.F.P., Antananarivo, Madagascar. 23 pp.
  • Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan, 248 pp.

Sources of illustration

  • Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
  • de Winter, B., de Winter, M. & Killick, D.J.B., 1966. Sixty-six Transvaal trees. Botanical Research Institute, Pretoria, South Africa. 175 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.

Author(s)

  • R.H.M.J. Lemmens, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article

Lemmens, R.H.M.J., 2006. Acacia galpinii Burtt Davy. 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 12 December 2017.