Amomum (PROSEA)

Plant Resources of South-East Asia
Introduction

Protologue: Fl. Ind. 1: 317 (1820); Pl. Coromandel 3: 75 (1820).

Family: Zingiberaceae

Chromosome number: x= 24; A. aculeatum:n= 24, A. krervanh: 2n= 48, A. longiligulare: 2n= 48, A. squarrosum:n= 24, A. uliginosum:n= 24, A. villosum: 2n= 48, A. xanthioides: 2n= 48

Major species

Amomum krervanh Pierre ex Gagnep.,
A. villosum Lour.,
A. xanthioides Wallich ex Baker.

Vernacular names

Thailand: krawaan
Vietnam: sa nhân.

Origin and geographic distribution

Amomum consists of about 100 species and is distributed in eastern Asia, from India and China, throughout the Malesian region, to tropical Australia. In Vietnam 22 species have been found. The total number of species in Malesia is difficult to estimate, but Peninsular Malaysia has approximately 18 species, Java about 13, and Borneo about 30; the distribution of the genus in other areas is very incompletely known.

Uses

Several Amomum species (for instance A. krervanh, A. villosum and A. xanthioides) are well known medicinal herbs in China, Indo-China and Thailand, particularly their fruits. They are mainly used to treat gastric and digestive disorders (e.g. vomiting, poor appetite, poor digestion, colic, diarrhoea). Besides their tonic, carminative and stomachic properties, the fruits are also considered to have emmenagogue and febrifugal properties. They are also sometimes prescribed to treat tuberculosis with hemoptysis, liver and uterine affections, and rheumatism. Seeds of A. villosum are known as "saren" in China, and the fruit shells as "sake". Some medicinal uses have been reported from the Malesian region; Amomum seeds are often included in stomachics and in preparations for coughs and colds.

The fruits of several species are commonly used as cooking ingredient, and are sometimes also used in perfumery. They may serve as antioxidant in foods.

Production and international trade

The fruits have importance in southern China (Yunnan). The total cultivated area is estimated to be over 13 000 ha. Around 1993 the dried fruits of A. villosum had a value of US$ 5.5/kg. Vietnam exports seed to China yearly, e.g. of A. villosum and A. xanthioides. In Cambodia, the fruits are mainly collected from the natural forest, whereas in Thailand the plants are mainly cultivated.

Properties

Fruits contain an essential oil, which is colourless and transparent and has the characteristic odour of the fruit and the seed. The fruits of A. krervanh contain approximately 3-4% essential oil with 1,8-cineol (eucalyptol) as main compound (60-80%). Further constituents are camphene, p-cymene, α-humulene, limonene, α-pinene, terpinene and α-terpineol. The pharmacological activities reported for A. krervanh include antifungal, antipyretic, smooth muscle relaxant and hypotensive activity. Fruits of A. villosum are reported to contain 3% essential oil consisting of bornylacetate (34%), camphor (27%), borneol (13%), camphene (10%), limonene (7%) and the minor compounds α- and β-pinene and myrcene.

Fruits of A. xanthioides contain 1.7-3% oil. The essential oils from A. xanthioides can be divided into 3 groups, based on the nature of their main compounds; the first group mainly containing camphor and bornylacetate, the second one mainly composed of linalool and nerolidol, and the third one with a high content of β-caryophyllene. The oil of the first group in general consists of camphor (29%), bornylacetate (22%), camphene (13.5%), limonene (10%), myrcene (4%), β-pinene (4%) and α-pinene (3%).

Investigations of A. villosum cultivated in Yunnan (China) revealed the presence of ethyl-octacosate, docosyl hexylate, stigmast-4-ene-1,3-dione, β-sitosterol and daucosterol in the roots and rhizomes.

A diterpene peroxide has been isolated from A. krervanh fruits in Thailand. This compound exhibited potent activity against Plasmodium falciparum and is thus of interest in combating malaria. In vitro experiments showed that the compound has roughly one-tenth the activity of artemisinin (from Artemisia annua L.) and the same level of activity as arteflene, which is an effective synthetic antimalarial agent structurally related to artemisinin. It is interesting to note that A. fenzlii Kurz is used to treat malarial fever in India, as is A. tsao-ko Crevost & Lem. in China.

Crude drugs prepared from A. xanthioides showed antifungal activity using organic solvents. At 3000 ppm the Indian A. subulatum Roxb. showed 100% inhibition for the storage fungus Aspergillus flavus; it showed a broad range of fungitoxicity in tests with plant pathogens, and had no adverse effect on the germination of rice; the seed oil was also highly active against keratinophilic fungi. A. subulatum also showed some insecticidal activity against the storage pest Sitophilus oryzae.

It has been reported from the Andaman Islands that sap of an Amomum species (doubtfully identified as A. aculeatum) acts as a tranquillizer for bees (rock bees, Apis dorsata), and is used in harvesting honey. When a mangled stem is held near the bee hives, the sap tranquillizes the vindictive worker bees to such an extent, that they do not sting. Reportedly, the sap's tranquillizing effect is specific to rock bees.

Adulterations and substitutes

Fruits and seeds of several other Zingiberaceae (e.g. Alpinia , Elettaria and Globba species) are used for similar purposes, and are sometimes mixed with Amomum seeds, but often they are less valuable.

Description

Medium-sized to large aromatic herbs up to 400 cm tall, with creeping rhizome near the soil surface or above ground, occasionally elevated on short stilt roots, sometimes emitting long stolons, several-stemmed; spurious stems erect, swollen near base.
Leaves distichous, numerous, usually lanceolate, finely veined, distinctly or indistinctly petiolate, lower ones sheathing with the sheath open on the side opposite the lamina, sheath apically produced into an erect, short or long ligule.
Inflorescence either lateral immediately from the rhizome near the base of a leafy stem, or lateral on stolons arising from the rhizome, capitulate, usually globose to ovoid, sometimes elongate; peduncle often short and shallowly hidden under earth or litter, with biseriate, persistent scales; bracts often numerous, arranged spirally, persistent or becoming slimy and disappearing, each bract embracing one usually tubular-sheathing bracteole and one flower.
Flowers bisexual, zygomorphic, 3-merous; calyx tubular, indented on one side, unequally 3-dentate on the other side; corolla with tube shorter to longer than calyx and lobes about as long as tube, superior lobe broadest and hollowed near apex, lateral lobes appressed against the labellum; labellum longer than corolla-lobes, very variable, lower part erect, tubular and connate with base of filament, upper part spreading, essentially 3-lobed and folded over the stamen, usually yellow or orange in the centre and with purplish markings, the sides often white; functional stamen 1, usually with distinct filament, anther elongate with connective developed into a large 3-lobed appendage, staminodes 2, small or absent; ovary inferior, 3-locular with axile placentation, style filiform with nectaries at base, stigma widened at apex, fimbriate.
Fruit berry-like or capsular, indehiscent or dehiscent with 3 valves, aculeate, ribbed or smooth, many-seeded.
Seeds angular, surrounded by an aril.

Growth and development

When cultivated, Amomum usually forms a dense ground cover. Plants are shallow-rooted, with about 80% of the root mass in the upper 10 cm of the soil. Flowering and fruiting start 4-5 years after planting.

The flowers, which usually last less than one day, are pollinated by insects, whose numbers and frequency of visits seriously affect seed production. Shedding of young fruits can be serious but can be reduced by proper use of 2,4-D and colchicine at the time of flowering. The fruits ripen in 3-4 months.

Other botanical information

Amomum belongs to the tribe Alpinieae, which also includes the small genus Elettaria, the large genus Alpinia, and the medium-sized genus Riedelia, which is centred in New Guinea.

A. compactum Soland. ex Maton is mainly cultivated for its seeds, which are used as a condiment, but it also has medicinal properties. A. subulatum Roxb. and A. fenzlii Kurz are used medicinally in India and Nepal. A. tsao-ko Crevost & Lem., whose fruits are used as a condiment, is also applied in traditional medicine in northern Vietnam and southern China. Its fruits are mixed with other medicinal plants to produce a reputed remedy for malaria. A. cardamomum L. is a synonym of Elettaria cardamomum (L.) Maton; several parts of this spice are used medicinally.

Ecology

Like other members of the Zingiberaceae, Amomum is almost a characteristic element of the ground flora of primary rain forest, often in moist locations and in lower montane forest (in Vietnam even up to 2200 m altitude). Amomum is humid-thermophilous and moderately shade tolerant, but intolerant of drought. The climatic conditions most suitable for A. villosum are 1000-2400 mm annual rainfall, about 80% relative humidity and a mean annual temperature of 19-22°C. It prefers loose, moist and humus-rich soils with a pH 6-7.5. These requirements seem to be applicable to many other Amomum spp.

Most Amomum-underplanted forests are located in valleys or on hillsides with a moderate slope at 500-1400 m altitude. The fruit production of A. krervanh in the lowland is inferior to that in the highlands.

Propagation and planting

In southern China, Amomum is preferably propagated by cuttings from stolons of 1-2-year-old plants with 2 horizontal branches. These cuttings may produce 3-4 shoots in the first year and 20-30 stems/m² within 3 years, which are ready for flowering and fruiting. Plants propagated from cuttings flower approximately 1 year earlier than seedlings. Sometimes rhizomes for planting are collected from the natural forest.

In southern China, shade-tolerant Amomum spp. like A. villosum are underplanted either in natural forest or as part of an agroforestry system. In natural forest, planting of seedlings or cuttings is preceded by thinning to give 30-40% light intensity, with retention of shade trees. In agroforestry, Amomum spp. are planted in plantations of rubber (Hevea brasiliensis (Willd. ex A.L. Juss.) Muell.-Arg.), Cinnamomum porrectum (Roxb.) Kosterm., mango (Mangifera indica L.), Albizia chinensis (Osbeck) Merr., Paraserianthes falcataria (L.) Nielsen and Cassia siamea Lamk. Satisfactory results were obtained by planting A. villosum seedlings or cuttings at 1 m × 1 m in 4 years old rubber plantings, spaced at least 6 m × 6 m.

Husbandry

Newly planted Amomum must be weeded frequently. In China, the application of fertilizer containing traces of manganese sulphate often effectively prevents leaf yellowing in A. villosum plantations.

Diseases and pests

Leaf blight of A. villosum caused by Glomerella cingulata occurs in China. Other diseases reported to affect A. villosum include seedling anthracnose (caused by Colletotrichum zingiberis) and fruit rot (caused by Rhizoctonia solani and Fusarium spp.). The insect pest Prodioctes sp. seriously affects cultivated A. compactum in West Java.

Harvesting

Fruits are usually hand-picked when they start darkening.

Yield

The mean annual yield of A. villosum planted in natural forest in southern China is about 375 kg/ha, with a maximum of 650 kg/ha. A 1-ha plot of A. villosum underplanted in rubber yielded about 190 kg/year of dried fruits.

Handling after harvest

After harvest fruits need to be dried immediately. To avoid the quality reduction of the seed and the oil evaporating rapidly they should not be peeled until after drying. Dried seeds are kept in jute or nylon bags stored in cool, dry and well-ventilated conditions. In Thailand, the volatile seed oil is obtained by water distillation.

Genetic resources and breeding

Many Amomum species seem to have a limited geographical distribution, but lack of botanical knowledge might be at least partly responsible for this. Most Amomum species occur in primary rain forest, and large-scale destruction of this forest type undoubtedly puts them at risk of genetic erosion or even extinction.

There is great market demand for Amomum in Indo-China and China, and natural populations are dwindling rapidly. A. villosum had become so scarce in China by the mid 1980s that considerable areas have since been planted with this species. In Vietnam and elsewhere, the scope for cultivation is increasing, which helps to protect Amomum species from genetic erosion.

Prospects

Although Amomum has a considerable reputation in Chinese medicine, it is not much used medicinally in South-East Asia. Little research has been done on the pharmacological characteristics, and more is needed to confirm the claimed medicinal properties. The antimalarial activity of fruit extracts of some Amomum species deserves further attention.

The successful cultivation of Amomum spp. in agroforestry systems in tropical China might also be applicable to South-East Asia, if there is a potential market for their products. The annual revenue from an agroforestry system of rubber and Amomum in tropical China is about 4 times that of a pure rubber plantation.

A thorough taxonomical revision of Amomum is badly needed. The species most interesting medicinally, now often cultivated in Indo-China and Thailand, could probably also be cultivated at higher elevations in Malesia.

Literature

Backer, C.A. & Bakhuizen van den Brink, R.C., 1968. Flora of Java. Vol. 3. Noordhoff, Groningen, the Netherlands. pp. 51-58.
Dao Lan Phuong, 1990. Chemical composition of Vietnamese Amomum xanthioides essential oil. Tap chi Duoc hoc [Journal of Pharmacy] 1: 17-19 (in Vietnamese).
Do Tat Loi, 1995. Medicinal plants and ingredients of Vietnam. Science and Technology Publishing House, Hanoi, Vietnam. pp. 516-523 (in Vietnamese).
Dutta, T.R., Ahmed, R., Abbas, S.R. & Rao, M.K.V., 1985. Plants used by Andaman aborigines in gathering rock-bee honey. Economic Botany 39(2): 130-138.
Ho Phamh, 1993. Zingiberaceae. Cay co Vietnam [Flora of Vietnam]. Vol. 3(1). Mekong Printing, United States. pp. 535-571.
Holttum, R.E., 1950. The Zingiberaceae of the Malay Peninsula. Gardens' Bulletin Singapore 13(1): 1-249.
Kamchonwongpaisan, S. et al., 1995. An antimalarial peroxide from Amomum krervanh Pierre. Tetrahedron Letters 36(11): 1821-1824.
Perry, L.M., 1980. Medicinal plants of East and Southeast Asia. Attributed properties and uses. The MIT Press, Cambridge, Massachusetts, Unites States & London, United Kingdom. pp. 437-438.
Smith, R.M., 1985. A review of Bornean Zingiberaceae: 1 (Alpineae p.p.). Notes from the Royal Botanic Garden Edinburgh 42(2): 261--314.
Zhou, S., 1993. Cultivation of Amomum villosum in tropical forests. Forest Ecology and Management 60(1-2): 157-162.

Selection of species

Authors

Nguyen Quoc Binh