669

19: Essential-oil plants

Ocimum gratissimum L.

Sp. pl.: 1197 (1753).

LABIATAE

2n = 40, (48, 64)

Ocimum viridiflorum Roth (1800), Ocimum suave Willd. (1809), Ocimum viride Willd. (1809).

Shrubby basil, East Indian basil, Russian basil (En). Menthe gabonaise (Fr). Indonesia: kemangi hutan, ruku-ruku rimba (Sumatra), selaseh mekah. Malaysia: selaseh besar, ruku-ruku hitam. Cambodia: ling leak kranam. Thailand: kaphrao-chang, horapha-chang, yira. Vietnam: h[uw][ow]ng nhu tr[aws]ng, [es] l[as] l[ows]n.

Ocimum gratissimum is found throughout the tropics and subtropics, both wild and cultivated. Its greatest variability occurs in tropical Africa (from where it possibly originates) and India. In South-East Asia it is cultivated mainly as a home garden crop, only in Vietnam is it grown on a commercial scale as well.

Ocimum gratissimum is grown for the essential oil in its leaves and stems. Eugenol and to a lesser extent thymol extracted from the oil are substitutes for clove oil and thyme oil. In Indonesia (Sumatra) a tea is made from the leaves, while in Thailand the leaves are applied as a flavouring. In Indonesia the eugenol-type of Ocimum gratissimum is used in the ceremonial washing of corpses and is planted in graveyards. In India Ocimum gratissimum, named 'ram tulsi', is widely used in religious ceremonies and rituals. The whole plant and the essential oil have many applications in traditional medicine, especially in Africa and India. Preparations from the whole plant are used as stomachic and in treating sunstroke, headache and influenza. The seeds have laxative properties and are prescribed against gonorrhoea. The essential oil is applied against fever, inflammations of the throat, ears or eyes, stomach pain, diarrhoea and skin diseases. It is being tested as an antibiotic. The essential oil is also an important insect repellent. Ocimum gratissimum is also cultivated as a hedge plant.

As the essential oil of Ocimum gratissimum is mainly a substitute for clove oil or thyme oil, it is rarely traded internationally. Its main use is in countries where import of the latter oils is difficult. Worldwide its annual production is currently estimated at 50 t, valued at US$ 0.8 million.

The fresh aboveground parts of Ocimum gratissimum contain 0.8—1.2% essential oil. The chemical composition of the oil is variable and at least 6 chemotypes have been reported, characterized by the main component of the essential oil: eugenol, thymol, citral, ethyl cinnamate, geraniol and linalool. An overview of the occurrence of the various types and possible implications for the taxonomy is lacking. The eugenol type is the most important economically; the thymol type was formerly important, but most thymol is now produced synthetically, while natural thymol is mostly obtained from Thymus vulgaris L. or Trachyspermum ammi (L.) Sprague ex Turrill. The other types are of little economic importance.
The eugenol-type oil is a brownish-yellow to pale yellow liquid with a powerful, warm-spicy and aromatic odour, reminiscent of clove oil, but with a sweet-woody, almost floral top note. The dry-out is more bitter than that of clove oil. Analysis of a sample of an essential oil of the eugenol type from Vietnam indicated that the main component was eugenol (71%) with small amounts of D-germacrene and (Z)-'BETA'-ocimene. In a sample from southern China the eugenol content was as much as 95%. Samples from Madagascar had eugenol contents of 40—90%, with very variable other components.
The thymol-type oil is a dark yellow to orange-yellow or brownish liquid with a medicinal-spicy, warm and somewhat herb-like odour. Its flavour is warm, slightly astringent and burning, and has a sweet medicinal aftertaste. Analysis of several samples of essential oils from Ocimum gratissimum from Central and West Africa rich in thymol indicated that their main constituents were thymol, 'GAMMA'-terpinene, p-cymene and eugenol. The concrete obtained by solvent extraction is much richer in thymol than the distilled oil. A geraniol-rich type, found in the United States, contained mainly geraniol (84—88%) with small amounts of 'GAMMA'-muurolene, neral, 'BETA'-caryophyllene and limonene. The citral type, reported from Iran, Pakistan and India is rich in citral (67%) and geraniol (26%). See also: Composition of essential-oil samples.

Aromatic, perennial herb, 1—3 m tall; stem erect, round-quadrangular, much branched, glabrous or pubescent, woody at the base, often with epidermis peeling in strips. Leaves opposite; petiole 2—4.5 cm long, slender, pubescent; blade elliptical to ovate, 1.5—16 cm x 1—8.5 cm, membranaceous, sometimes glandular punctate, base cuneate, entire, margin elsewhere coarsely crenate-serrate, apex acute, puberulent or pubescent. Inflorescence a verticillaster, arranged in a terminal, simple or branched raceme 5—30 cm long; rachis lax, softly pubescent; bracts sessile, ovate, 3—12 mm x 1—7 mm, acuminate, caducous; pedicel 1—4 mm long, spreading or ascending, slightly curved; flowers in 6—10-flowered verticillasters, small, hermaphrodite; calyx 2-lipped, 2—3 mm long, in fruit 5—6 mm, pubescent, upper lip rounded and recurved, reflexed in fruit, lower lip with 4, narrow, pointed teeth, central pair of teeth minute and much shorter than the upper lip; corolla campanulate, 3.5—5 mm long, 2-lipped, greenish-white, pubescent outside, upper lip truncate, 4-fid, lower lip longer, declinate, flat, entire; stamens 4, declinate, in 2 pairs, inserted on the corolla tube, filaments distinctly exserted, upper pair with a bearded tooth at the base; ovary superior, consisting of 2 carpels, each 2-celled, style 2-fid. Fruit consisting of 4, dry, 1-seeded nutlets enclosed in the persistent calyx (the lower lip closing the mouth of the fruiting calyx); nutlet subglobose, 1.5 mm long, rugose, brown; outer pericarp not becoming mucilaginous in water.

In a growth trial in Colombia, germination of Ocimum gratissimum was very poor (<10%); cuttings took 28 days to take root. Flowering started after 136 days and continued until 195 days. Seed matured after 259 days. Flowering and seed set were much poorer than in Ocimum basilicum L. or Ocimum minimum L. In South-East Asia flowers can be found year-round.
In northern India, oil content of young plants was low (2.3%) until the seed setting stage, then remained constant at 2.8% until the seed maturation stage.

Ocimum gratissimum is a variable polymorphic complex species, often subdivided into subspecies, varieties and formas, mainly based on differences in chemical content, the morphology of the fruiting calyx, and on different degrees of hairiness, but the variation forms a continuum. Sometimes Ocimum gratissimum (existing chromosome counts: 2n = 40, 48, 64), Ocimum suave (2n = 32, 48, 64) and Ocimum viride (2n = 38, 40) (here treated as one complex species Ocimum gratissimum) are considered as three different species. Although more research is needed it seems certain that those three taxa are closely related and have 10 homologous chromosomes in common. Crosses between Ocimum gratissimum and Ocimum viride resulted in partially fertile F₁ hybrids. Variability is greatest in Africa and India. In Java, 2 chemotypes exist, the eugenol and the thymol type, respectively described as Ocimum gratissimum L. forma caryophyllatum Backer and forma graveolens Backer. Forma caryophyllatum is characterized by: leaves clove-scented when bruised, upper side short-haired, lower side densely gland-dotted, bracts 4—6 mm long, much longer than wide, lower lip of corolla not flushed with violet; and forma graveolens by: leaves strongly odoriferous but not clove-scented when bruised, upper surface covered with minute hairs, bracts 2—4 mm long, about as long as wide, lower lip of corolla flushed violet inside.
Most Ocimum species contain essential oil but are primarily used as vegetable (e.g. hoary basil, Ocimum americanum L.), as spice (e.g. sweet basil, Ocimum basilicum L.), or as vegetable and medicine (e.g. sacred or holy basil, Ocimum tenuiflorum L.).

In its native area Ocimum gratissimum occurs from sea-level up to 1500 m altitude in coastal scrub, along lake shores, in savanna vegetation, in submontane forest, and disturbed land. In South-East Asia it is not frequently found in open locations like roadsides and clearings, but more often cultivated as a hedge plant, up to about 300 m altitude.

Ocimum gratissimum is propagated by seed or cuttings. The time for transplanting seedlings into the field in the delta of the Hong River in northern Vietnam is February—March, in southern Vietnam from May—August. Plants are spaced at about 40 cm x 50 cm. The optimum harvesting time for distillation of the essential oil is when 3 branches per plant or 75% of the branches are flowering. In northern Vietnam 2—3 cuts can be obtained in an average year, 4—5 cuts per year in the south. In Vietnam, Ocimum gratissimum remains productive for 5—10 years.

In India, yields of 70—75 t/ha green herbage of Ocimum gratissimum producing 400 l essential oil in 2 years have been obtained experimentally. In Thailand harvesting every 10—12 days resulted in an annual green herbage yield of only 13 t/ha and an oil yield of nearly 200 l.

After harvesting the aboveground parts of Ocimum gratissimum the plants are left to wilt in the shade for a few days and are then steam-distilled to extract the essential oil.

Germplasm collections of Ocimum L., including Ocimum gratissimum are being maintained at the National Biological Institute, Bogor (Indonesia) and at the North Central Regional Plant Introduction Station, Ames, Iowa (United States). Hardly any breeding work has been done.

The essential oil obtained from Ocimum gratissimum may serve as a substitute for oils of higher quality and value. It is therefore unlikely that its importance will increase.

Charles, D.J. & Simon, J.E., 1992. A new geraniol chemotype of Ocimum gratissimum L. Journal of Essential Oil Research 4: 231—234.
De Medici, D., Pieretti, S., Salvatore, G., Nicoletti, M. & Rasoanaivo, P., 1992. Chemical analysis of essential oils of Malagasy medicinal plants by gas chromatography and NMR spectroscopy. Flavour and Fragrance Journal 7: 275—281.
Dung, N.X., Leclercq, P.A., Moi, L.D. & Thai, N.T.P., 1987. About the chemical composition of the essential oil from Ocimum of Vietnam, and dynamical accumulation of essential oil in Ocimum basilicum L. var. basilicum. Proceedings of the NCSR of Vietnam. Vol. 1(2). pp. 27—34.
Guenther, E., 1952. The essential oils. Vol. 3. D. Van Nostrand, New York, United States. pp. 424—428.
Khosla, M.K., 1989. Chromosome meiotic behaviour and ploidy nature in genus Ocimum (Lamiaceae), 'Sanctum group'. Cytologia 54: 223—229.
Khosla, M.K., 1995. Study of inter-relationship, phylogeny and evolutionary tendencies in genus Ocimum. Indian Journal of Genetics 55: 71—83.
Ntezurubanza, L., Scheffer, J.J.C. & Baerheim Svendsen, A., 1987. Composition of the essential oil of Ocimum gratissimum grown in Rwanda. Planta Medica 53: 421—423.
Paton, A., 1992. A synopsis of Ocimum L. (Labiatae) in Africa. Kew Bulletin 47: 403—435.
Podimuang, V., 1980. Kaprao oils. Witthayasat Maha Witthayalai Khon Kaen [Journal of Science and Arts of the Khon Kaen University] 8: 42—49.
Zhu, L.-F, Li, Y.-H., Li, B.-L, Lu, B.-Y., Xue, N.H. & Zhang, W.-L., 1993. Aromatic plants and essential constituents. Hai Feng Publishing Company, Hong Kong, China. p. 99 & Suppl. 1, p. 62.

Diah Sulistiarini

Sulistiarini, D., 1999. Ocimum gratissimum L.. In: L.P.A. Oyen and Nguyen Xuan Dung (Editors): Plant Resources of South-East Asia No 19: Essential-oil plants. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea