Prota 7(1): Timbers/Bois d’œuvre 1
Engl. & Prantl, Nat. Pflanzenfam. III, 3: 319 (1894).
Papilionaceae (Leguminosae - Papilionoideae, Fabaceae)
2n = 40
Herminiera elaphroxylon Guill. & Perr. (1832).
Ambatch, ambach, pith tree, balsa wood tree (En).
Origin and geographic distribution
Aeschynomene elaphroxylon occurs widely in tropical Africa, from Senegal east to Ethiopia and Kenya and south to Zambia, Angola and Mozambique; also in Madagascar, but there probably introduced. It has been introduced in Egypt, Indonesia and Sri Lanka.
The lightweight wood is used for canoes, rafts and shields, but also for building poles and furniture. The stems are used for fishing-net floats and sandals. The wood is attached to fishing spears to ensure they reappear at the water surface in case of a miss, or may be attached to spears to serve as a buoy.
The pale coloured and spongy wood is very light, with a density of 160–190 kg/m³ at 15% moisture content.
Large shrub or small tree up to 9(–12) m tall; stems swollen, pithy, glandular hairy and with woody prickles up to 1.5 cm long, often with dense mats of adventitious roots; outer bark green, smooth. Leaves alternate, paripinnately compound with 9–20 pairs of leaflets; stipules broadly ovate, 10–13 mm long, auricled on one side; petiole and rachis together 4–16 cm long, densely bristly hairy and with short prickles; leaflets oblong, 8–26 mm × 4–10 mm, obliquely rounded at base, truncate or slightly notched at apex, glabrous above, shortly hairy below. Inflorescence an axillary raceme up to 4.5 cm long, 1–4-flowered; bracts ovate, up to 7 mm long, bracteoles broadly ovate, up to 16 mm long. Flowers bisexual, papilionaceous; pedicel 12–16 mm long; calyx glandular hairy, 2-lipped, the upper lobe 2–2.5 cm long and entire to slightly notched, the lower lobe 1.5–2 cm long and shallowly 3-toothed; corolla with rounded, notched, orange yellow standard up to 4.5 cm in diameter and yellow wings and keel; stamens 10, fused into a sheath split into 2 groups of 5; ovary superior, 1-celled, style slender, upturned. Fruit a spirally coiled pod 10–14 cm long when unrolled, glandular hairy, 6–17-jointed. Seeds kidney-shaped, up to 8 mm in diameter, dark purplish brown.
Aeschynomene comprises about 150 species, tropical America and Africa being richest in species, with a few species in tropical Asia. Continental Africa has about 50 species, Madagascar 13. The stems and wood of some other Aeschynomene species is used for similar purposes as those of Aeschynomene elaphroxylon.
The stems of Aeschynomene crassicaulis Harms, a shrub with procumbent stems occurring from Senegal east to DR Congo, are used as floats for fishing nets and lines, and as fuel and fodder, whereas the leaves are added to a mixture of other plants to treat rheumatism.
The stems of Aeschynomene cristata Vatke, a shrub widespread in tropical Africa including Madagascar, are also used as floats for fishing nets and in raft and canoe construction, and parts of the plant are applied to skin complaints.
Aeschynomene pfundii Taub. closely resembles Aeschynomene elaphroxylon, but is a smaller shrub without prickles. It occurs at watersides from Mali east to Kenya and south to Zambia. Its stems are used as floats for fishing nets.
Aeschynomene elaphroxylon is adapted to fluctuating water levels. At the base of the bole unbranched roots up to 10 cm long are found as well as larger roots of unlimited length growth. The plants root superficially into the soil, and whole thickets are frequently displaced in the water by wind or currents. Numerous hemispherical protuberances are situated on the stem bark containing nitrogen-fixing bacteria of the genus Bradyrhizobium. Aeschynomene elaphroxylon usually flowers at the beginning of the rainy season.
Aeschynomene elaphroxylon occurs at lakesides and in pools and swamps, up to 1350 m altitude. The lower part of the stem is often submerged, and Aeschynomene elaphroxylon is well suited to seasonally flooded localities where the soil remains wet. The stems and branches may form dense floating masses that clog watercourses.
Genetic resources and breeding
Aeschynomene elaphroxylon is widespread and locally common and not endangered by genetic erosion, although locally it has disappeared due to changed climatic conditions, e.g. in most parts of Lake Chad.
The wood of Aeschynomene elaphroxylon and other Aeschynomene species will remain of local importance because of its great floating ability. It could be a good substitute for the wood of balsa (Ochroma pyramidale (Cav. ex Lam.) Urb.) for special applications such as model making. Aeschynomene elaphroxylon deserves more attention as a nitrogen fixing tree that is potentially useful for enhancing soil fertility in temporarily flooded agricultural land, e.g. as a green manure in rice cultivation.
• Arbonnier, M., 2004. Trees, shrubs and lianas of West African dry zones. CIRAD, Margraf Publishers Gmbh, MNHN, Paris, France. 573 pp.
• Burkill, H.M., 1995. The useful plants of West Tropical Africa. 2nd Edition. Volume 3, Families J–L. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 857 pp.
• du Puy, D.J., Labat, J.N., Rabevohitra, R., Villiers, J.-F., Bosser, J. & Moat, J., 2002. The Leguminosae of Madagascar. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 750 pp.
• Jenik, J. & Kubikova, J., 1969. Root system of tropical trees 3. The heterorhizis of Aeschynomene elaphroxylon (Guill. et Perr.) Taub. Preslia 41: 220–226.
• Alazard, D., 1991. La nodulation caulinaire dans le genre Aeschynomene. Thèse de doctorat, Université Claude Bernard, Lyon, France. 146 pp.
• Alazard, D. & Duhoux, E., 1988. Diversity of stem nodulation sites in Aeschynomene spp. Journal of Plant Physiology 132: 123–125.
• Beentje, H.J., 1994. Kenya trees, shrubs and lianas. National Museums of Kenya, Nairobi, Kenya. 722 pp.
• Eggeling, W.J. & Dale, I.R., 1951. The indigenous trees of the Uganda Protectorate. Government Printer, Entebbe, Uganda. 491 pp.
• Ita, E.O., 1994. Aquatic plants and wetland wildlife resources of Nigeria. CIFA (Committee for Inland Fisheries of Africa) Occasional Paper No 21. FAO, Rome, Italy. 52 pp.
• Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 pp.
Correct citation of this article:
Lemmens, R.H.M.J., 2007. Aeschynomene elaphroxylon (Guill. & Perr.) Taub. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.