Macaranga (PROSEA Medicinal plants)

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Plant Resources of South-East Asia
Introduction
List of species


Macaranga Thouars

Protologue: Gen. Nov. Madag.: 26 (1806).
Family: Euphorbiaceae
Chromosome number: x= 11; M. denticulata, M. tanarius:n= 11

Origin and geographic distribution

Macaranga comprises some 250 species. About 30 of these occur in tropical Africa and Madagascar, the rest in tropical Asia, from India, Sri Lanka and Burma (Myanmar), through Indo-China, southern China, Taiwan, the Ryukyu Islands, Thailand and throughout the Malesian region, to northern Australia and the Pacific, east to Fiji. The main centre of diversity is found within Malesia where about 160 species occur, with an exceptionally high number of endemics in Borneo and New Guinea.

Uses

Roots, bark and leaves of Macaranga are fairly commonly used internally in traditional medicine in South-East Asia, usually as a decoction, to treat stomach-ache, dysentery, haemoptysis, cough and fever. The leaves, and sometimes resin, are applied externally to wounds, ulcers, sores and boils.

In Brunei leaves of M. beccariana Merr. are used in a post-natal bath and as a repellent for ants. Some species are used in traditional medicine in Fiji, e.g. to treat convulsions, diarrhoea and as an abortifacient; an example is M. vitiensis Pax & Hoffm. Several Macaranga species are used medicinally in Africa. Bark and leaves of M. barteri Müll. Arg. are used as a vermifuge, febrifuge, aperient and anti-anaemic tonic, and to treat cough, bronchitis and gonorrhoea. A decoction of the roots of M. heterophylla (Müll. Arg.) M√ºll. Arg. is applied against amenorrhoea, and as an emmenagogue and abortifacient, a decoction of the bark to treat cough, and a decoction of the leaves to treat gonorrhoea. The bark of M. hurifolia Beille is used as a purgative and against cough, and a decoction of the roots to treat oedema. The bark and roots of M. spinosa Müll. Arg. are administered to treat asthma, cough, headache, rheumatism and for liver and stomach complaints, whereas a decoction of the bark is applied to toothache and thrush.

The wood is frequently used, especially for parts of houses not in contact with the ground, but also for e.g. light framing, interior trim, moulding, shingles, packing cases and match splints. It yields a high-quality pulp and produces excellent particle board, cement-bonded board and wood-wool board, and is suitable for the production of plywood. It provides good fuelwood.

The bark and pith or the fruit of several Macaranga species produce a resin or gum that can be used as glue. The bark of some species has been used to tan fishing nets. Bark, leaves and fruits of some species are applied in the Philippines in the preparation of a fermented drink called "basi" made from sugar cane. Large leaves, as found in several species, are used to wrap food.

Properties

Several tannins including corilagin, furosin, geraniin and macaranganin have been isolated from Macaranga, and many medicinal properties are probably due to these tannins. No less than 28 tannins have been demonstrated in M. tanarius leaves, and 10 in the bark. The results of tests with M. tanarius roots from Taiwan indicate that they may have immunopotentiating effect of humoral immune response in mice. An aqueous ethanol extract exhibited antiviral activity against ranikhet and vaccinia virus.

The bark and leaves of M. gigantea and M. triloba showed moderate antimicrobial activity against Staphylococcus aureus, Escherichia coli, Saccharomyces cerevisiae and Fusarium oxysporum. It is assumed that gallotannin is the substance in M. grandifolia fruits (which are added to "basi") that inhibits the growth of lactic acid bacteria.

Four prenylated flavanones with antibacterial activity have been isolated from the dichloromethane extract of leaves of M. pleiostemon Pax & Hoffm., a species from New Guinea. An aqueous leaf extract of M. peltata (Roxb.) Müll. Arg. from India inhibited conidial germination of the fungus Drechslera oryzae.

A chloroform extract of M. carolinensis Volk. from the Caroline Islands showed in-vitro cytotoxic activity against P-388 and 9KB cell lines. Geranyl stilbenes with cytotoxic activity have been isolated from the African M. schweinfurthii Pax.

Botany

  • Evergreen, dioecious, small to medium-sized trees up to 30(-40) m tall; bole straight, up to 50(-70) cm in diameter, occasionally with stilt roots, rarely with buttresses; bark surface smooth or rough with lenticels, hoop-marked, stripping off easily, greyish to pinkish, inner bark pink to reddish-brown; crown open, often bluish-green.
  • Leaves arranged spirally, simple, often prominently lobed, palmately or pinnately veined, the main veins joined by parallel, concentric veinlets giving the effect of spider-webbing, often peltate; petiole often long and kneed; stipules often large and persistent.
  • Inflorescence an axillary panicle, raceme or spike, consisting of small clusters.
  • Flowers small, subtended by often glandular bracteoles, with 2-5-lobed perianth (petals absent); male flowers with 1-20 stamens having 3-4-celled anthers; female flowers with superior, (1-)2-3(-6)-celled ovary, styles usually free and unlobed.
  • Fruit a leathery or woody, often shouldered capsule, smooth to variously spiny, splitting into 2-valved parts leaving the central column, few-seeded.
  • Seeds black, often with a thin orange to red aril.
  • Seedling with epigeal germination; cotyledons emergent, leafy; hypocotyl elongated; all leaves arranged spirally, conduplicate to involute.

Macaranga species are short-lived pioneers becoming 15-20 years old. Most species develop according to Rauh's architectural model, characterized by a monopodial trunk with rhythmic growth and so developing tiers of branches that are themselves morphogenetically identical with the trunk. Trees may flower when very young, and flowering and fruiting are fairly regular, several times a year. A few species are either facultative or obligate myrmecophytes. The latter group of species provides specific nesting space, mainly hollow twigs, for ants of the genus Crematogaster. The ants protect the plants from herbivores.

The dimorphism of sapling leaves and those of mature trees renders identification difficult. Macaranga is closely related to Mallotus, but differs in its 3-4-celled anthers and more conspicuously in its lateral inflorescences and the absence of stellate hairs.

Ecology

Most Macaranga species are pioneers and form a characteristic of secondary forest especially along roadsides in western Malesia and New Guinea, but are less common in Sulawesi, the Moluccas and Java. They are often found gregariously and may locally form pure stands. A few species are found in primary forest. Most species thrive in a per-humid climate, some also under slightly seasonal conditions. The altitudinal range is large, with a few species occurring up to almost 3000 m altitude in New Guinea.

Management

Macaranga can be propagated by seed. For M. tanarius there are about 54 500 dry seeds/kg. Seeds of M. tanarius show about 50% germination in 24-72(-265) days, whereas those of M. triloba have about 80% germination in 19-37 days. It is, however, difficult to get seedlings to grow.

Genetic resources

Some Macaranga species are narrow endemics, but the genetic resources of most species are not endangered as trees are common and characteristic elements of secondary vegetation.

Prospects

Macaranga is commonly used in traditional medicine throughout the large area of distribution of the genus, and often for similar purposes, e.g. internally to treat stomach-ache, dysentery, cough and fever, and externally to treat wounds and ulcers. However, surprisingly little is known about active compounds and pharmacological properties, and more research is worthwhile.

The fairly general occurrence of Macaranga and the long wood fibres make the exploitation for pulp and paper and the production of wood-based panels promising in the near future.

Literature

120, 121, 542, 883.

Selection of species

Authors

  • S. Aggarwal