Populus ilicifolia (PROTA)

Plant Resources of Tropical Africa Introduction

List of species

General importance
Geographic coverage Africa
Geographic coverage World
Timber
Conservation status

Populus ilicifolia (Engl.) Rouleau

Protologue: Rhodora 47: 362 (1945).

Family: Salicaceae

Vernacular names

Tana River poplar (En).

Origin and geographic distribution

Populus ilicifolia is endemic to eastern Kenya and north-eastern Tanzania.

Uses

The boles of Populus ilicifolia trees are used to make dug-out canoes. They are the first choice of Pokomo people for canoes, and these were often sold down the Tana River to fishermen on the coast. These canoes were very common in the Malindi-Lamu area of Kenya and were often taken aboard sea-going dhows for use as dinghies. The wood is also used for poles, posts, utensils and beehives. Populus ilicifolia is suitable for the production of plywood. The wood is used as firewood, but is of low quality for this purpose. The tree is useful for the stabilization of river banks and as ornamental. The foliage is eaten by livestock.

Properties

The wood is brown, with a coarse texture. It is lightweight, with a density of about 500 kg/m³ at 12% moisture content, and rather soft. The wood air dries well with some distortion and end checking. At 12% moisture content, the modulus of rupture is about 70 N/mm² and compression parallel to grain 36 N/mm². The wood is easy to saw and work. The durability of the wood is low. It has been reported that dug-out canoes last for up to 2 years.

Description

Deciduous, dioecious, medium-sized tree up to 25(–30) m tall; bole cylindrical; bark surface smooth and whitish to pale brown, but becoming longitudinally fissured and red-brown or grey-brown in older trees; crown conical to rounded, open; twigs longitudinally fissured, glabrous, reddish brown, with scattered lenticels. Leaves alternate, simple; stipules strap-shaped or obovate, up to 5 mm long, thin and reddish, deciduous; petiole (0.5–)2.5–4.5 cm long; blade angular ovate or obovate, on juvenile growth linear to narrowly elliptical, 4–7.5 cm × (0.5–)4–5 cm, base cuneate to rounded, apex acute to lobed, margins irregularly lobed or coarsely toothed, papery, glabrous or sparsely hairy, pinnately veined with 4–7(–8) pairs of lateral veins. Inflorescence a unisexual catkin; male inflorescence axillary, 1.5–2 cm long, 6–9-flowered; female inflorescence terminal on short branches, 1–4 cm long, 5–15-flowered. Flowers unisexual, in axils of spatulate bracts 3–6 mm long, lobed or toothed at apex, without perianth, disk thin, reddish, deeply fringed; male flowers with pedicel c. 1 mm long, stamens many, c. 1.5 mm long; female flowers with pedicel 3–5(–8) mm long, ovary ovoid, 3.5–5 mm long, hairy, style c. 1 mm long, stigmas 4, 6–7 mm long, 2–3-lobed. Fruit an ovoid capsule 0.5–1.5 cm × 0.5–1 cm, furrowed, rough with pale lenticels, dehiscent with 2–4 valves, many-seeded. Seeds ovoid, 1–2 mm long, with tuft of long white hairs.

Other botanical information

Populus comprises about 40 species, most of them confined to temperate and subtropical areas of the northern hemisphere. Populus ilicifolia is the only species of the genus that is a native to tropical Africa. Several Populus species and hybrids have been introduced in tropical Africa for timber and pulpwood production, or as ornamental. They are mostly grown in the highlands. Populus alba L. and Populus deltoides Marshall are most widely planted in tropical Africa. Both are medium-sized trees up to 30 m tall. The hybrid Populus ×canadensis Moench (Populus deltoides × Populus nigra L.) has been planted in Mauritius to serve as a windbreak.

Populus ilicifolia is a shade-intolerant pioneer species. It is short-lived, with a lifespan of about 50 years. Leaf fall is usually during the rainy season. It flowers irregularly, depending on moisture levels. Pollination is by wind. Ripe fruits are most common in August–December, and the seeds with their long hairs are widely dispersed by wind.

Ecology

Populus ilicifolia is found in riverine forest and woodland, and on sand banks and mud flats, from sea-level up to 1000 m altitude. It is most frequently encountered on low-lying sandy point bars that are frequently flooded, but it requires deep soils. The mean annual rainfall within the area of distribution is 200–800 mm and the mean day temperatures vary between 17°C and 35°C.

Management

Populus ilicifolia produces numerous seedlings on alluvial soils, but many of these are washed away by floods and damaged by grazing animals. It can be propagated by seed, wildlings, layering, and stem and root cuttings. For propagation by seed, fruits should be collected before they open. After opening of the fruits, the seeds are placed in seed trays filled with fine sand flooded with water. They germinate within a few days. They can also be stored for up to one year at 0°C.

Stem cuttings of 8–10 cm long and 1–2 cm in diameter are recommended; they should be kept moist and at about 25°C, rooting after 3–6 weeks. Root suckers can be planted, as is the case for other Populus spp. Trees coppice quite poorly. When they are planted as ornamental, it is recommended to keep some distance from buildings and pavements because of the large superficial roots and because trees are short-living with easily breaking branches. Intercropping with crops such as maize, rice, millet and banana is possible as the quite open tree crown gives little shade.

Seedlings are commonly attacked by blight and stem-rot caused by Fusarium, caterpillars of Phalantha butterflies and by scale insects. In larger-sized boles, heart rot is common.

Genetic resources

Populus ilicifolia is classified in the IUCN Red List as vulnerable because of its restricted distribution area and habitat degradation. However, as long as suitable habitats along rivers are available, it is not threatened because of its pioneer nature, regenerating easily on alluvial soils. Some collection of germplasm has been done in Kenya.

Prospects

Populus ilicifolia is a promising plantation tree comparable to other Populus spp. in temperate regions. Its rapid growth enables high production of wood, which is, however, not suitable for purposes where durability is required. The wood is suitable for similar purposes as that of other Populus spp., especially for boxes, crates, utensils, matches, veneer, plywood and pulp for paper production. The establishment of experimental plantations seems worthwhile, but the rather narrow ecological niche of Populus ilicifolia should be taken into consideration.

Major references

• Chikamai, B.N., Githiomi, J.K., Gachathi, F.N. & Njenga, M.G., undated. Commercial timber resources of Kenya. Kenya Forestry Research Institute (KEFRI), Nairobi, Kenya. 164 pp.

• Maundu, P. & Tengnäs, B. (Editors), 2005. Useful trees and shrubs for Kenya. World Agroforestry Centre - East and Central Africa Regional Programme (ICRAF-ECA), Technical Handbook 35, Nairobi, Kenya. 484 pp.

• Oballa, P.O., 1996. Status of Populus ilicifolia in Kenya. Occasional Paper No 3, Kenya Forestry Research Institute, Nairobi, Kenya. 36 pp.

• Oballa, P., Meroka, D., Wambui, B. & Wakori, S., 1996. Genetic variation within Populus ilicifolia Roleau. International Poplar Commission Session 20. FAO, Rome, Italy. 6 pp.

• Wilmot-Dear, C.M., 1985. Salicaceae. In: Polhill, R.M. (Editor). Flora of Tropical East Africa. A.A. Balkema, Rotterdam, Netherlands. 7 pp.

Other references

• Beentje, H.J., 1994. Kenya trees, shrubs and lianas. National Museums of Kenya, Nairobi, Kenya. 722 pp.

• Dale, I.R. & Greenway, P.J., 1961. Kenya trees and shrubs. Buchanan’s Kenya Estates Limited, Nairobi, Kenya. 654 pp.

• Johansson, S., 1991. Ecological implications for Tana River Basin forestry and irrigated agriculture. In: Trevor, P. & Baxter, W. (Editors). When the grass is gone: development intervention in African arid lands. SIAS Seminar Proceedings 25: 114–140.

• Maingi, J.K. & Marsh, S.E., 2006. Composition, structure, and regeneration patterns in a gallery forest along the Tana River near Bura, Kenya. Forest Ecology and Management 236(2-3): 211–228.

• Marais, W., 1985. Salicacées. In: Bosser, J., Cadet, T., Guého, J. & Marais, W. (Editors). Flore des Mascareignes. Familles 161–169. The Sugar Industry Research Institute, Mauritius, l’Office de la Recherche Scientifique Outre-Mer, Paris, France & Royal Botanic Gardens, Kew, Richmond, United Kingdom. 3 pp.

• Meikle, R.D., 1989. Salicaceae. In: Hedberg, I. & Edwards, S. (Editors). Flora of Ethiopia. Volume 3. Pittosporaceae to Araliaceae. The National Herbarium, Addis Ababa University, Addis Ababa, Ethiopia and Department of Systematic Botany, Uppsala University, Uppsala, Sweden. pp. 258–260.

• Njoroge, G.N., Kaibui, I.M., Njenga, P.K. & Odhiambo, P.O., 2010. Utilisation of priority traditional medicinal plants and local people’s knowledge on their conservation status in arid lands of Kenya (Mwingi District). Journal of Ethnobiology and Ethnomedicine 6: 22.

• van Wyk, B.E. & Gericke, N., 2000. People’s plants: a guide to useful plants of southern Africa. Briza Publications, Pretoria, South Africa. 351 pp.

• Weiss, E.A., 1973. Some indigenous trees and shrubs used by local fishermen on the East African coast. Economic Botany 27(2): 175–192.

• Wilmot-Dear, C.M., 1991. Salicaceae. In: Launert, E. & Pope, G.V. (Editors). Flora Zambesiaca. Volume 9, part 6. Flora Zambesiaca Managing Committee, London, United Kingdom. pp. 120–124.

Author(s)

• C.H. Bosch, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

• L.P.A. Oyen, PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

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

Correct citation of this article

Bosch, C.H. & Oyen, L.P.A. & Lemmens, R.H.M.J., 2012. Populus ilicifolia (Engl.) Rouleau. In: 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. Accessed 6 March 2025.

• See the Prota4U database.