Grewia (PROSEA)

Plant Resources of South-East Asia
Introduction

Protologue: Sp. pl. 2: 964 (1753); Gen. pl., ed. 5: 412 (1754).

Family: Tiliaceae

Chromosome number: x= 9; G. abutilifolia Vent. ex Juss.: n= 9, G. asiatica: 2n= 36, G. hirsutaVahl: n= 9, G. laevigata: n= 9

Vernacular names

Indonesia: talok (general), darowak (Sundanese)
Malaysia: chenderai (general), bunsi (Iban, Sarawak), damak-damak (Peninsular)
Philippines: danglin (Filipino)
Burma (Myanmar): tayaw
Thailand: po-lai, po-muen, yap
Vietnam: cây long man duc, cò ke.

Origin and geographic distribution

Grewia comprises about 200 species and is confined to the Old World tropics. The genus extends north to the Himalayas, China and Taiwan, east to Tonga and Samoa and south to northern Australia. It occurs throughout the Malesian region where about 30 species are found.

Uses

The wood of Grewia is generally used for small articles where toughness is required, like tool handles, spades, shafts of golf sticks, shoulder poles for carrying small loads, pestles, bows, billiard cues and shingles. In the Philippines it is regarded as a good substitute for "lanutan" (Hibiscus campylosiphon Turcz.) used for vehicle bodies.

The fibrous bark is used to make ropes. The fruits of most species are edible.

The leaves of several species are used medicinally, chiefly for external applications. In Thailand stem decoctions of Grewia are used to treat acne and food poisoning, and root decoctions as a febrifuge and diuretic. Leaves, roots and fruits are used to treat various complaints in India. In Timor (Indonesia) a paste of grated bark from a Grewia species has been externally applied to bruises; for internal afflictions an infusion of grated bark was drunk.

G. asiatica L., well known as fruit and timber tree, is also used medicinally. Its fruits are considered a remedy for throat problems and the bark is applied as a demulcent, especially for urogenital afflictions.

Production and international trade

As the size of the timber is generally small and the supply is limited, the wood of Grewia is used on a local scale only.

Properties

Grewia yields a medium-weight to heavy hardwood with a density of 730-900 kg/m³ at 15% moisture content. Heartwood pale grey to pale brown, not sharply differentiated from the sapwood; grain interlocked; texture fine; wood with some silver grain. Growth rings indistinct, sometimes indicated by paler-coloured tissue; vessels very small to medium-sized, solitary, in radial multiples of 2-4 and in clusters, solitary vessels usually round and open; parenchyma paratracheal vasicentric, narrow, visible with a hand lens, and apotracheal in marginal or seemingly marginal bands; rays moderately fine to moderately broad, rather conspicuous on radial surface; ripple marks absent, although very fine ripple marks evident on radial surface due to storied parenchyma and fibres.

The wood seasons well. It is moderately soft to moderately hard, tough and moderately strong. The wood works satisfactorily with hand and machine tools. It is non-durable when exposed to the weather or in contact with the ground, but durable for interior use. Under cover, the heartwood is moderately resistant to dry-wood termites and the sapwood is susceptible to Lyctus .

See also the table on microscopic wood anatomy.

An alcohol extract of whole G. hirsuta plants showed diuretic activity in rats. It also showed central nervous system-depressant activity, antiviral activity against Ranikhet disease, and antibacterial activity against Staphylococcus aureus at an LD₅₀ value exceeding 1000 mg/kg. Alkaloids, phenolic and steroidal compounds have been detected in the leaves.

Botany

Evergreen or deciduous shrubs or small trees up to 15 m tall or rarely climbers; bole frequently poorly shaped, up to 35 cm in diameter, without buttresses; bark surface smooth to shallowly fissured, sometimes obscurely hoop-marked, grey-brown, inner bark fibrous, pale cream. Indumentum of stellate and simple hairs.
Leaves alternate, distichous, entire, serrate or double serrate, 3- or 5-veined from the base, often whitish below; stipules entire or divided.
Inflorescence an axillary or sometimes terminal cyme arranged in a panicle.
Flowers bisexual, regular, 5-merous; sepals free; petals shorter than the sepals or sometimes absent, whitish or yellowish; stamens many, on a raised torus; ovary superior, (1-)2(-5)-locular with 2-8 ovules in each cell, style with a thickened or lobed stigma.
Fruit a fleshy or pulpy drupe, usually 2-4-lobed, with 1-4 pyrenes containing 1-2 seeds.
Seedling with epigeal germination; cotyledons emergent, leafy; hypocotyl elongated; all leaves alternate or sometimes the first pair subopposite.

Most of the species flower and fruit in the second half of the year, some bear flowers and fruits throughout the year. Maturation of the fruits takes about 1-2 months. The fruits are eaten by birds which may thus disperse the seeds.

Various authors disagree about whether the genera Grewia and Microcos should be united or kept separate. The main differences between the two are the unlobed stigma, the terminal paniculate inflorescence, the involucral bracts and the unlobed fruit of Microcos versus the thickened or lobed stigma, the often axillary inflorescence, the absence of involucral bracts and the usually lobed fruit of Grewia.

Ecology

Grewia species are fairly common elements of the understorey of primary and secondary, deciduous or evergreen, lowland to montane forest, up to 1700 m altitude. They are also found in open dry deciduous forest, scrub vegetation, forest edges and hedges, where they may be encountered as pioneers. They occur on a wide variety of soil types.

Silviculture

Grewia may be raised from seed, whereas G. asiatica can also be propagated vegetatively by cuttings, layering and budding. G. eriocarpa has been recommended for afforestation in the dry regions of the Lesser Sunda Islands, where it appears spontaneously in regenerating woodland. Its natural regeneration is generally good, but it is not resistant to fire.

Genetic resources and breeding

Grewia species are generally not threatened by harvesting or cutting, as they are only seldom used, often occur in secondary vegetation and even exhibit a weedy nature. They are incidentally grown in botanical gardens.

Prospects

Grewia wood is only used for special purposes and will remain important in this respect.

Little is known about the pharmacological properties of South-East Asian Grewia. Some of their traditional uses, e.g. as a diuretic, are corroborated in animal tests, but the vast majority of their many uses in Ayurvedic medicine are not yet supported by modern research.

Literature

61, 70, 161, 163, 164, 188, 192, 209, 218, 235, 267, 436, 438, 672, 772, 780, 861, 887, 889, 934, 963, 974, 1038, 1039, 1164, 1169, 1221, 1222. timbers

121, 249, 334, 449, 483, 662, 883. medicinals

Selection of species

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Authors

Wongsatit Chuakul, Noppamas Soonthornchareonnon & Orawan Ruangsomboon