Croton megalocarpus (PROTA)

Plant Resources of Tropical Africa Introduction

List of species

General importance
Geographic coverage Africa
Geographic coverage World
Vegetable oil
Carbohydrate / starch
Dye / tannin
Medicinal
Timber
Ornamental
Forage / feed
Auxiliary plant
Climate change

Croton megalocarpus Hutch.

distribution in Africa (wild)

1, tree habit; 2, flowering twig; 3, seeds. Redrawn and adapted by Achmad Satiri Nurhaman

Protologue: Oliv., Fl. trop. Afr. 6(1): 760 (1912).

Family: Euphorbiaceae

Vernacular names

• Croton (En).
• Msenefu (Sw).

Origin and geographic distribution

Croton megalocarpus occurs from eastern DR Congo east to Kenya and south to Malawi, Zambia and Mozambique.

Uses

The wood, most commonly known as ‘musine’, is used for construction, flooring, stools, mortars, beehives, veneer and plywood. It is suitable for joinery, interior trim, ship building, vehicle bodies, furniture, cabinet work, railway sleepers and agricultural implements. It is also used as firewood and for charcoal production.

A maceration or decoction of the bark is taken as a vermifuge, and to treat whooping cough, pneumonia, stomach-ache, fever including malaria, and abdominal complaints associated with gall bladder and spleen problems. Sap from leaves and young twigs are applied to wounds. An infusion of the powdered bark with potash is given to goats as a conditioner. Although trees are usually not browsed by livestock, leafy twigs may serve as forage for goats. Seeds are used as poultry feed. Seed oil is tested as bio-fuel. The seeds can be used to dye wool yellowish. The flowers provide nectar for honey bees; the honey produced is dark and has a strong flavour. Croton megalocarpus is planted in hedges, live fences, shelterbelts and windbreaks, and as an ornamental shade tree. It may serve as shade tree for coffee plantations. The foliage provides good mulch. The fruit shells are used as mulch in vegetable gardens and as a component of potting mixtures.

Production and international trade

There are no trade statistics for Croton megalocarpus timber, which is only used locally. However, it has been used for flooring in the United Kingdom. In recent years, Croton megalocarpus has gained interest for large-scale planting programmes as a commercial poultry feed and bio-fuel crop with low agro-ecological demands, mainly in Kenya and Tanzania. Most of the plantations are still in the pilot stage of development.

Properties

The heartwood is yellowish white to brownish grey, often with irregular dark brown streaks, and not distinctly demarcated from the 2.5–5 cm wide sapwood. The grain is usually straight, texture medium. Freshly sawn wood has an unpleasant smell.

The wood is medium-weight, with a density of 700–750 kg/m³ at 12% moisture content. It is liable to splitting and moderate distortion during air drying. Once dry, it is often not stable in service, especially when used in larger sizes. At 12% moisture content, the modulus of rupture is about 97 N/mm², compression parallel to grain 52 N/mm², Janka side hardness 6000 N and Janka end hardness 7560 N.

The wood is easy to saw and work with hand tools, but moderately difficult to machine. It usually planes to a smooth and lustrous surface. It is resistant to abrasion. The nailing, screwing, gluing, varnishing, painting and jointing properties are all satisfactory. The wood is only suitable for sliced veneer. It is moderately durable, being slightly susceptible to termite, dry-wood borer and marine borer attacks. It is liable to attacks by blue stain fungi. It is easy to impregnate with preservatives under pressure. Dry sawdust may irritate nose and throat in wood workers. It has been reported that smoke from the wood irritates the eyes.

Seeds have an oil content of about 30% and a protein content of about 50%. The oil has purgative activity and also showed Epstein-Barr virus activating potency. Bark extracts showed weak antibacterial activity in in-vitro tests. From the bark the clerodane diterpene chiromodine has been isolated as a major constituent, together with lupeol, betulin, β-sitosterol and long-chain fatty esters. Ground seeds showed good results in preliminary tests as chicken feed with no adverse effects on production and hatchability of eggs.

Adulterations and substitutes

As an oil producer for bio-fuel, Croton megalocarpus is comparable to jatropha (Jatropha curcas L.), which has become the focus of large-scale planting programmes in several tropical countries on account of its potential as a bio-fuel crop with low agro-ecological demands.

Description

• Medium-sized to fairly large tree up to 35 m tall; bole cylindrical, branchless for up to 20 m, up to 100(–120) cm in diameter; bark surface densely longitudinally fissured, rough, cracking, pale grey-brown, inner bark yellowish or pale brown; crown spreading, flat, with branches in layers; twigs densely scaly.
• Leaves alternate, simple and entire; stipules linear-filiform, 0.5–1 cm long; petiole 2–8(–11) cm long, densely scaly; blade ovate to elliptical-ovate or oblong-lanceolate, (4–)7–14(–19) cm × (1.5–)3–7(–11) cm, cuneate to rounded or shallowly cordate at base, with 2(–4) basal glands, shortly acuminate at apex, thickly papery to thinly leathery, scaly at both surfaces, silvery below, pinnately veined with 15–25 pairs of lateral veins.
• Inflorescence a terminal pendulous raceme up to 30 cm long, densely scaly, completely male or with a few female flowers at base.
• Flowers unisexual, regular, 5-merous, yellowish; pedicel 0.5–1.5 cm long; calyx with triangular-ovate lobes up to 4.5 mm × 3.5 mm; petals free, c. 5 mm long; male flowers with obovate petals, free disk glands and 25–30(–40) free stamens up to 8 mm long; female flowers with linear petals, annular to shallowly 5-lobed disk, superior, globose to slightly 3-lobed ovary c. 4 mm in diameter, and 3 shortly 2-fid styles.
• Fruit an ellipsoid-ovoid to globose capsule 2.5–4.5 cm long, scaly, greyish brown, with thick, woody endocarp, dehiscent from the apex, 3-seeded.
• Seeds ellipsoid-ovoid to oblong-ellipsoid, flattened, 2–2.5 cm long, slightly ridged and rough, whitish to grey-brown.

Other botanical information

Croton comprises about 1200 species and occurs throughout the warmer parts of the world. It is best represented in the Americas; about 65 species occur in continental Africa and about 125 in Madagascar.

The wood of several other Croton species is used in tropical Africa, but none of them is important.

In Ghana the wood of Croton penduliflorus Hutch., a small to medium-sized tree up to 20 m tall, is used for rafters. But is is also a medicinal plant.

Croton longiracemosus

In DR Congo the wood of Croton longiracemosus Hutch., a medium-sized tree up to 30 m tall with bole up to 40 cm in diameter, is used for construction, whereas in Congo the leaves are eaten as a tonic and applied to maturate furuncles.

Croton wellensii

In Gabon the whitish wood of Croton wellensii De Wild., a medium-sized tree up to 25(–30) m tall with bole up to 45(–80) cm in diameter, is used for stools.

Croton dichogamus

In Kenya the wood of Croton dichogamus Pax, a shrub or small tree up to 7.5 m tall, is used in building huts. The roots and stems are used to flavour food and drinks. Roots and sometimes leaves are used in traditional medicine to treat colds, fever, tuberculosis and syphilis, and as a tonic.

Croton megalobotrys

In southern Africa the whitish wood of Croton megalobotrys Müll.Arg., a small tree up to 15 m tall with bole up to 60 cm in diameter, is considered useful for unspecified purposes. The bark and seeds have some reputation as a treatment for malaria, whereas roots and bark are used as purgative and to treat ascites and female sterility. Leaves are used to treat body pain and seeds as vermifuge.

Anatomy

Wood-anatomical description (IAWA hardwood codes):

• Growth rings: 1: growth ring boundaries distinct.
• Vessels: 5: wood diffuse-porous; (10: vessels in radial multiples of 4 or more common); 13: simple perforation plates; 22: intervessel pits alternate; (23: shape of alternate pits polygonal); 27: intervessel pits large (≥ 0 μm); 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 42: mean tangential diameter of vessel lumina 100–200 μm; 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; 69: fibres thin- to thick-walled.
• Axial parenchyma: 76: axial parenchyma diffuse; 77: axial parenchyma diffuse- in-aggregates; 78: axial parenchyma scanty paratracheal; 86: axial parenchyma in narrow bands or lines up to three cells wide; 92: four (3–4) cells per parenchyma strand; 93: eight (5–8) cells per parenchyma strand.
• Rays: 97: ray width 1–3 cells; 104: all ray cells procumbent; (113: disjunctive ray parenchyma cell walls present); 115: 4–12 rays per mm.
• Mineral inclusions: 136: prismatic crystals present; 138: prismatic crystals in procumbent ray cells; (139: prismatic crystals in radial alignment in procumbent ray cells).

(P. Mugabi, P.E. Gasson & E.A. Wheeler)

Growth and development

Croton megalocarpus grows rapidly when conditions are favourable. In Kenya seedlings reached 1.7 m tall in one year, and in Rwanda 3 m in 2 years and 11.5 m in 5 years. In Burundi planted trees reached on average only 3.6 m tall 7 years after planting, and 15 m tall with a bole diameter of 24 cm after 32 years. Trees may already start flowering when they are 4 years old. The flowers are short-lived. They are pollinated by insects such as bees. Fruits take about 5 months to ripen after flowering. The seeds are eaten by birds including poultry.

Ecology

Croton megalocarpus occurs in evergreen and semi-deciduous forest at (700–)900–2100(–2400) m altitude, sometimes also in riverine woodland and wooded grassland. It is most commonly found in regions with a mean annual rainfall of 900–1900 mm, with a dry season of 3–4 months and a mean annual temperature of 11–26°C. It prefers light, deep and well-drained soils.

Propagation and planting

Natural regeneration is often prolific, Croton megalocarpus being a pioneer of large forest gaps and forest margins. It has been reported to become invasive under favourable climatic conditions. It is usually propagated by sowing, either directly into the field or in pots. There are 1000–1700 seeds per kg. The germination rate of fresh seed is up to 95% after 45 days. Mature fruits can be collected from the ground. Seed can be extracted after cracking the fruit wall and should be sun dried to 5–9% moisture content. The high oil content of the seed (about 30%) makes storage difficult, but seed can be stored in plastic containers up to 1 year at 3°C; a germination rate of 80% can then still be reached. Traditionally farmers prepare 8 cm deep furrows where they drop ripe fruits 15–20 cm apart. When seedlings are raised in seed beds, they should be lightly shaded and initially watered twice a day. Croton megalocarpus is sometimes propagated by wildlings and stump planting is also practised.

Management

Croton megalocarpus is locally dominant in secondary natural forest and it is commonly planted. On slopes of Mount Kenya, Croton megalocarpus has been found on 40% of the farms at an average density of 15 trees per farm. It is also retained after forest clearing as a shade tree for crops such as coffee and sugar cane, but it may provide too much shade for maize cultivation.

The tree can be managed by lopping, pollarding and coppicing. When planted in hedges, plants should be pruned for the first time after 2 years. Croton megalocarpus trees develop a deep taproot. This makes them quite drought tolerant and allows food crops to be grown underneath.

Harvesting

Fruits are most commonly collected from the ground underneath the trees and seeds are separated manually. Simple tools in the form of a tin with a notch have been developed. However, many fruits collected from the ground do not contain viable seeds. Plant parts used for medicinal purposes are harvested throughout the year when the need arises. They can be used immediately or are dried and stored for later use.

Yield

Preliminary observations indicate that a yield of 25–30 kg of seed per tree per year is realistic.

Handling after harvest

The presscake remaining after oil extraction can be incorporated in high-calorie and high-protein supplements in chicken feed, and also as bio-fuel and as organic fertilizer. Oil extraction from the seed is done by hand-operated or mechanized screw presses. The oil may be refined in a continuous transesterification reactor to produce bio-fuel of diesel oil quality and glycerol as a valuable by-product.

Genetic resources

Croton megalocarpus is quite widespread, both in the wild and planted, and is not in danger of genetic erosion. Systematic germplasm collection or preservation programmes do not seem to exist.

Breeding

No breeding work has been undertaken yet. The most important selection criteria would be long and straight boles for timber production and high oil yield of the seeds. Most plant material used so far is derived from simple selection within semi-wild populations or landraces. Great variance has been observed in seed production, related to frequency of flowering, number of inflorescences, number of female flowers per inflorescence, number of seeds per fruit and seed weight. This indicates that through selection and breeding oil yields could be considerably increased.

Prospects

Croton megalocarpus is a multipurpose tree that is important for people as a source of timber, firewood and medicine, and as auxiliary plant. It is already an important component of agroforestry systems in East Africa. Types with large and straight boles might be interesting for timber plantations, but research on silvicultural and propagation aspects is still needed. Seeds seem to have great potential as a source of protein for poultry feed and perhaps also feeds for other livestock, but more research is still needed on the phytochemistry and possible adverse effects before it can be developed into an important export product. However, oil production for bio-fuel seems to be most promising, and already large investments are being made to establish large-scale plantations in East Africa. Breeding work is needed to select types with high oil production and optimal management methods of plantations need to be established. Possibilities of vegetative propagation including tissue culture techniques have to be explored to enable rapid and large-scale multiplication of good-quality genetic material. At the end of their productive life in bio-fuel plantations, approximately 50 years after planting, trees can be felled for their timber.

Major references

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• CAB International, 2005. Forestry Compendium. Croton megalocarpus. [Internet] http://www.cabicompendium.org/ fc/datasheet.asp?CCODE=CVN_M4. August 2009.

• 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.

• Katende, A.B., Birnie, A. & Tengnäs, B., 1995. Useful trees and shrubs for Uganda: identification, propagation and management for agricultural and pastoral communities. Technical Handbook 10. Regional Soil Conservation Unit, Nairobi, Kenya. 710 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.

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Other references

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Sources of illustration

• Noad, T. & Birnie, A., 1989. Trees of Kenya. A fully illustrated field guide. Nairobi, Kenya. 281 pp.

• Teel, W., 1984. A pocket directory of trees and seeds in Kenya. Kenya Energy Non-Governmental Organisations, Nairobi, Kenya. 151 pp.

Author(s)

• A. Maroyi, Botany Department, Rhodes University, Box 94, Grahamstown 6140, South Africa

Correct citation of this article

Maroyi, A., 2010. Croton megalocarpus Hutch. [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.

Accessed 18 December 2024.

• See the Prota4U database.