Cymbopogon flexuosus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

1, habit; 2, part of inflorescence branch; 3, lower glume of sessile spikelet.

Cymbopogon flexuosus (Nees ex Steudel) J.F. Watson

Protologue: in Atkins., Gaz. N.W. Prov. India 10: 392 (1882).

Family: Gramineae

Chromosome number: 2n= 20 (diploid), 40 (tetraploid)

• Andropogon flexuosus Nees ex Steudel (1854),
• A. nardus L. var. flexuosus (Nees ex Steudel) Hackel (1889),
• Cymbopogon travancorensis Bor (1954).

• East Indian lemongrass, Malabar grass, Cochin grass (En).
• Herbe de Malabar (Fr)
• Vietnam: sả dịu.

C. flexuosus possibly originates from India (Western Ghats) but it is also native in Burma (Myanmar) and Thailand. It is also often cultivated as a garden plant throughout the tropics as well as in its native area. In South-East Asia it is commonly cultivated and sometimes naturalized (e.g. in Indonesia in Java, Bali and Sumbawa). Cultivation is most important in India, Indonesia and Madagascar.

Distillation of the leaves of C. flexuosus yields East Indian lemongrass oil. The oil is very similar to West Indian lemongrass oil and is used as a flavouring and fragrance material, mainly in soaps, detergents and industrial perfumes. The oil is a source of citral, which is either used directly or converted toα- andβ-ionones. Lemongrass oil is applied as a fumigant against flies and mosquitoes, although the repellent action is rather poor. Spent grass is dried and used to fuel the distillery, as animal feed, or returned to the field as manure. C. flexuosus is also planted to control erosion and sometimes it is used as a source of cellulose and for paper production.

In trade statistics hardly any distinction is made between the 2 major sources of lemongrass oil: West Indian lemongrass (C. citratus (DC.) Stapf) and East Indian lemongrass (C. flexuosus). In 1986 world production of lemongrass oil was estimated at 650 t, valued at about 4.3 million US$, most of the oil originating from Central and South America (Argentina, Brazil, Guatemala, Honduras). In 1992-1994 average annual import of lemongrass oil in the United States was 80 t and the price per kg averaged US$ 7.35. Most East Indian lemongrass oil is produced and used in India, but there are no reliable production and trade statistics.

East Indian lemongrass oil is a yellow or amber-coloured, somewhat viscous liquid with a strong, sweet, fresh-grassy, citral and lemon-like, herbaceous or tea-like odour. The main chemical constituent of the oil is citral, which is a mixture of the stereoisomers geranial (50%) and neral (30%); minor components include limonene, linalool, geraniol and myrcene. The oil from C. flexuosus is more soluble in alcohol and is said to be of better quality than West Indian lemongrass oil from C. citratus (DC.) Stapf.

East Indian lemongrass oil has been approved for food use by the Food and Drug Administration of the United States under paragraph 182.20 and "generally recognized as safe" (GRAS No 2627). See also: Composition of essential oil-samples and the Table on standard physical properties.

Lemongrass oil is rarely adulterated; the citral content being the quality criterion of overriding importance. The essential oil from Litsea cubeba (Lour.) Persoon is an important alternative source of natural citral. Occasionally, the oil is adulterated with synthetic citral.

• Perennial, tufted, aromatic grass with numerous erect culms arising from a short, thick rhizome. Culm (stem) up to 2.5(-3) m tall, terete, solid, reddish or whitish, smooth and glabrous but often short-bearded at the nodes.
• Leaves sheathing, glaucous-green, sometimes tinged purplish; sheath clasping the culm (lower sheaths very loose), striate, smooth and glabrous but densely hairy at the junction with the blade; ligule chartaceous, 2-5 mm long; blade linear-acuminate, tapering at both ends, about 1 m × 1.5 cm, apex attenuating to a long, filiform tip, minutely scabrid on both surfaces, coarsely scabrid on the margins, with densely tomentose triangular patches at the base of both surfaces.
• Inflorescence a large, loose, repeatedly branched panicle, up to 60 cm × 30 cm, with many long flexuous drooping branches; branches of highest order ending in a spatheole subtending a pair of racemes; axis up to 12-noded, internodes tomentose in upper part, nodes villous; spatheole narrowly elliptical-acuminate, 1-2 cm long; peduncle 3-3.5 mm long, wiry, smooth and glabrous.
• Racemes 15-20 mm long, one subsessile, the other stalked, very hairy in the fork, bearing pairs of spikelets, 1 of each pair sessile, the other pedicellate.
• Sessile spikelet subcylindrical with acute apex, 4.5-5 mm long, with a short bearded callus; lower glume size and shape of the spikelet, 2-keeled from the middle upwards, winged on the keels, smooth, scabrid on the margins of the keels, 1-3 veined; upper glume boat-shaped, 4.5-5 mm long, keeled in the upper third, winged and scabrid on the keel; lower floret reduced to an empty lemma; upper floret hermaphrodite with a narrow lemma cleft to the middle and bearing an awn 10-12 mm long, palea absent, 2 truncate-cuneate lodicules, stamens 3, styles 2 with plumose, purple stigmas.
• Pedicelled spikelet male or sterile, elliptical-acuminate, 3.5-4 mm long; lower glume many veined, glabrous; upper glume boat-shaped, 3-veined, glabrous.

In areas with a cold winter C. flexuosus perennates through its rhizomes and resumes growth in spring. The root system is extensive but not deeply penetrating into the soil. C. flexuosus is a short-day plant and flowering is common. In tropical India at low elevation flowering starts in November; at higher elevations flowering is delayed by 2-3 months. Flowering starts in the middle of the panicle and proceeds upward and downward, taking about 1 month before the whole panicle has flowered. Most flowers open in the early morning; cross pollination is normal because of the protogynous nature of the bisexual florets. In commercial production only selected plants are allowed to flower for seed production because profuse flowering prior to cutting substantially reduces oil yield. Normally plants become (4-)6-8 years old.

C. flexuosus is rather variable and several varieties have been distinguished on the basis of the size and degree of compactness of the panicle; this has little practical value, however, as many intermediates occur. The characteristics of C. flexuosus most useful for distinguishing it from other species are its ample panicle with drooping branches, its crowded raceme pairs with its small sessile spikelets and its densely tomentose triangular patches at the base of the leaf blade. Based on the colour of the culm 2 forms can be distinguished: one reddish, the other whitish. All cultivars for essential oil production have reddish culms because the white-stemmed forms produce oil with a lower citral content. Sometimes the whitish form is considered as a separate species: C. travancorensis Bor.

Several cultivars have been developed in India. "Sugandhi" (OD 19) is the most popular and is adapted to a wide range of soils and to the northern Indian climate; plants tiller profusely, are up to 1.75 m tall and under rainfed conditions reach an oil yield of 80-100 kg/ha with 85-88% citral. "Pragati" (LS 48) is adapted to tropical and subtropical climates of northern India; the plants are tall with dark purple leaf sheaths, average oil content is 0.63% with 86% citral. "Cauvery" is a recently released high-yielding cultivar adapted to South Indian conditions. "Dhanrosa", also called "Thatha-1", is a high-geraniol selection from southern India, tentatively classified as C. flexuosus. It affords up to 10 harvests per year under irrigated conditions.

In north-eastern India and Nepal C. pendulus (Nees ex Steudel) J.F. Watson (Jammu lemongrass) is a locally important species which also produces a lemongrass oil. Several promising cultivars with high oil yield and citral content have been selected from it. All Jammu lemongrass oil is consumed locally.

C. flexuosus occurs naturally in fields, roadsides, in mixed deciduous, dipterocarp and teak forest, often on limestone, and on slopes and ridges at 100-2200 m altitude. It requires a warm, per-humid climate with ample sunshine, average daytime temperatures of 25-30°C with no extremely low night temperatures and 2500-3000 mm annual rainfall evenly distributed over the year. In drier areas growth is less luxuriant, but oil and citral content are higher. Long, dry, sunny periods, however, reduce oil content. In northern India, low temperatures inhibit growth during the winter and frost kills the plant. C. flexuosus is mostly grown up to 300 m altitude, but in Kerala State, India, it is grown up to 1000 m. It grows best on fertile sandy loams, but in Kerala it is mostly grown on poor lateritic soils on slopes. It requires a well-drained soil and waterlogging is not tolerated. Soil salinity up to EC 1 S/m has little influence on yield.

C. flexuosus is generally propagated by seed, as offshoots often fail to establish. Seed, usually produced in large amounts (100-200 g/plant), is sown very densely in nurseries; 10-12 kg seed is needed to produce seedlings for 1 ha. At the onset of the monsoon seedlings are transplanted in the 3-4-leaf stage, when 50-70 days old, topped to 15-20 cm and dipped in fungicide. A close spacing of 15 cm × 15 cm is recommended to suppress weed growth, but farmers often plant at a wider spacing. Direct sowing in the field is also practised, for which about 35 kg seed/ha is needed, but this often results in very heavy weed infestation. C. flexuosus may be interplanted with other crops but it is generally the major component when grown for oil.

Although C. flexuosus is a vigorous crop, 2-3 weedings are required after transplanting, followed by a weeding in the first month after each harvest. In direct-sown crops early weeding should be more intensive. Annual earthing-up encourages tillering. In India fertilizer applications vary according to growing conditions; a general recommendation is to apply annually 30 kg/ha each of N, P₂O₅and K₂O plus 60 kg/ha N, in 3-4 split applications. Burning the dry grass and stubble at the end of the dry season is common in Kerala; it rejuvenates the crop and controls termite and stem borer attack. In Kerala C. flexuosus is grown as a rainfed crop; in northern India 4-6 irrigations are required during the dry season, i.e. between February and June.

Though several diseases are reported for C. flexuosus, none causes serious reduction in oil yield. Balansia sclerotica reduces seed yield, several Drechslera spp. and Curvularia spp. cause leaf-spot diseases, while in northern India smut caused by Tolyposporium christensenni or Ustilago andropogonis is common. Serious pests do not occur, but Chilo stem borer sometimes causes damage. It can be controlled by pesticides and by burning the stubble after the harvest. Young plantations should be protected from grazing by domestic stock especially when other forage is not available.

In southern India, harvesting rainfed C. flexuosus starts in May-June (about 6-8 months after planting) and cuts are taken every 6-7 weeks. If cut too early, the oil obtained is of very poor quality because of a very low aldehyde content. Usually 2-3 harvests can be taken during the year of planting and 4-6 harvests in subsequent years. At higher elevations fewer are possible. The leaves are cut, usually with a sickle, at 10-20 cm above the ground, preferably on sunny days when the leaves are dry.

The annual herbage yield of C. flexuosus in the first 2 years after planting is 15-20 t/ha in India. In subsequent years yields decline, the rate of decline being directly related to the standard of management and maintenance of soil fertility. Average oil yield in India is 0.2-0.5% from fresh herbage weight (on average about 75 kg/ha). Herbage harvested in the dry season usually has a much higher oil content (0.3-0.7%) than herbage harvested in the rainy season.

Wilting the herbage of C. flexuosus in the shade for up to 2 days and chopping it into pieces 3 cm long increases still efficiency and oil yield. Many end-users prefer oil distilled from fresh herbage, since it is said to have a finer odour than oil obtained from wilted or dried herbage. In India the leaves of C. flexuosus are generally distilled in small, scattered, primitive stills. Water distillation is commonly used, but direct and indirect steam distillation is applied in more modern plants. Distillation takes about 3 hours. In India a unit for 100 kg grass and 140 l water requires 2-2.5 hours to produce 0.35 kg oil, using 40 kg fuel wood. The oil deteriorates during prolonged storage, because of photo-oxidation. It should be protected from air, heat and sunlight. For conservation, indigenous antioxidants are added to the oil in India. An extract of betel leaves (Piper betle L.), for instance, maintains the citral content of the oil at 83% compared to 72% in non-treated oil.

Several institutions in South and South-East Asia are involved in germplasm collection and conservation of aromatic grasses. Systematic collection of germplasm of Cymbopogon was initiated at the Lemongrass Breeding Station, Odakkali, Kerala, India as early as 1951. The collection now has over 450 accessions. Other major institutions include: the Research Institute for Spice and Medicinal Crops (RISMC), Bogor, Indonesia; the Thailand Institute of Scientific and Technological Research (TISTR), Bangkok, Thailand; the University of the Philippines, Los Baños, the Philippines; the Central Institute of Medicinal and Aromatic Plants, Lucknow, India and the National Board of Genetic Resources, New Delhi, India.

Breeding work on C. flexuosus in India aims at higher herbage yields (especially of leaves) with improved oil and citral contents. These characters are all polygenic. Methods have been developed to obtain induced pollen sterility, including hot water treatment and application of malic hydrazide. Several new cultivars have been released by the Aromatic and Medicinal Plants Research Station, Odakkali (India) and the Central Institute of Medicinal and Aromatic Plants, Lucknow (India). Clones R8P6 and R16P3 were selected in Bangalore (India) having significantly higher essential oil contents than "Sugandhi". The essential oil content of clones PC5 and PC8 is only slightly lower than that of R8P6, but is less affected by seasonal temperature fluctuations.

The various essential oils of Cymbopogon are likely to retain an important place as low-price aroma chemicals for many products ranging from soaps to detergents and insect repellants. C. flexuosus remains the preferred lemongrass oil in perfumery in India; elsewhere oil from C. citratus is more highly valued.

• Boelens, M.H., 1994. Sensory and chemical evaluation of tropical grass oils. Perfumer and Flavorist 19: 29-45.
• Bor, N.L., 1953, 1954. The genus Cymbopogon Spreng. in India, Burma and Ceylon. Journal of the Bombay Natural History Society 51: 890-916 (Part 1, 1953); 52: 149-183 (Part 2, 1954).
• Kulkarni, R.N. & Ramesh, S., 1992. Development of lemongrass clones with high oil content through population improvement. Journal of Essential Oil Research 4: 181-186.
• Soenarko, S., 1977. The genus Cymbopogon Sprengel (Gramineae). Reinwardtia 9: 225-375.
• Thomas, J., 1995. Lemongrass. In: Chadha, K.L. & Rajendra Gupta (Editors): Advances in Horticulture. Vol. 11. Medicinal and aromatic plants. Malhotra Publishing House, New Delhi, India. pp. 717-733.
• Virmani, O.P., Srivastava, R. & Datta, S.G., 1979. Oil of lemongrass. Part 1: East Indian. World Crops 31: 72-74.
• Weiss, E.A., 1997. Essential oil crops. CAB International, Wallingford, United Kingdom. pp. 86-103.

East Indian lemongrass oil

• Relative density : 0.855-0.905
• Refractive index : 1.483-1.489
• Optical rotation : -3° to +1°
• Miscibility in ethanol : 1:3 (70%)
• ISO/EOA : ISO 4718 '98

See comments : Physical properties of essential oils (PROSEA)

Soenarko, S., 1977. The genus Cymbopogon Sprengel (Gramineae). Reinwardtia 9: 225-375. Fig. 39B, p. 366 (inflorescence branch, glume); Weiss, E.A., 1997. Essential oil crops. CAB International, Wallingford, United Kingdom. Fig. 4.8, p. 87 (photograph of habit). Redrawn and adapted by P. Verheij-Hayes.

L.P.A. Oyen