Ocimum americanum (PROSEA)
- Protologue: Cent. pl. 1: 15 (1755).
- Family: Labiatae
- Chromosome number: 2n= 24, possible occurrence of a polyploid series
- Ocimum africanum Lour. (1790),
- O. canum Sims (1823),
- O. brachiatum Blume (1826).
- Hoary basil, American basil (En)
- Indonesia: kemangi, serawung, selasih putih
- Malaysia: selaseh, kemangi, ruku-ruku
- Thailand: maenglak
- Vietnam: rau húng.
Origin and geographic distribution
O. americanum occurs wild and cultivated throughout tropical Africa and tropical Asia. Its exact origin is unknown. In South-East Asia it has been reported from the continental parts, from Indonesia and Papua New Guinea. Its occurrence in the Philippines is doubtful. It has also been introduced into tropical America and some islands of the West Indies.
Whereas sweet basil (O. basilicum L.), shrubby basil (O. gratissimum L.) and holy basil (O. tenuiflorum L.) are very fragrant and used as condiments, medicinal plants, or for ceremonial uses, O. americanum, being mild in flavour, is extensively cultivated in Indonesia, Malaysia and Thailand for the young leaves, which are eaten raw as a vegetable side-dish. The fragrant leaves are also added to various dishes with a fishy or disagreeable smell.
The nutlets swell in water into a gelatinous mass often used in sweet cooling drinks as can be done likewise with nutlets of O. basilicum.
In traditional medicine, hoary basil is used for several ailments. Decoctions are used for coughs, pounded leaves are placed on the forehead to relieve catarrh or on the chest for respiratory problems, the whole plant is used in baths to treat rheumatism, renal colic and calcifications. More recently, the plant has been listed as a potential medicine against cancer.
The essential oil of O. americanum is used in soap and cosmetics. It has been reported to exhibit fungitoxic properties (without phytotoxic side-effects). Hoary basil has been planted on a large scale in the Commonwealth of Independent States, Kenya and Pakistan for the production of camphor, which has medicinal and industrial applications (celluloid, fireworks).
Production and international trade
There are no statistics on the production of hoary basil for vegetable use, but it is locally important. It is an indispensable ingredient of Sundanese cuisine (West Java), often cultivated in home gardens and generally offered for sale on local markets.
Per 100 g edible portion, hoary basil contains: water 87 g, protein 3.3 g, fibre 2.0 g, Ca 320 mg, Fe 4.5 mg, and vitamin C 27 mg. The energy value is 180 kJ/100 g.
O. americanum contains citral, camphor, and methyl-cinnamate in varying proportions, leading to spicy odours like cinnamon, clove and lemon.
- An erect, much-branched, annual, aromatic herb, 0.3-1 m tall.
- Stem and branches quadrangular, yellowish-green, densely white-pilose in young parts, less so when older.
- Leaves simple, decussate, petiolate; petiole up to 2.5 cm long; leaf-blade lanceolate to elliptical, 2.5-5 cm × 1-2.5 cm, cuneate at base, margin entire, apex acute, glabrous, gland-dotted on both surfaces.
- Inflorescence up to 15 cm long, composed of decussate, 3-flowered cymes, appearing as 6-flowered whorls (verticillasters) up to 3 cm apart, terminal, simple or branched; peduncle and axis quadrangular; bracts elliptical-lanceolate, 2-3 mm long, hairy, persistent; pedicel up to 4 mm long, strongly recurved at top; calyx bilobed, in flower 2-2.5 mm long, in fruit 3-4.5 mm, villous inside, pubescent with long white hairs outside, upper lobe flat, suborbicular, lower lobe canaliculate, sharply 4-toothed at top; corolla tubular, 2-lipped, 4-6 mm long, white, upper lip strongly recurved at top and crenately 4-lobed, lower lip entire, smaller than upper lip; stamens 4, didynamous, slender and exserted; pistil with 4-ovuled and 4-lobed ovary, filiform style and 2-lobed stigma.
- Fruit composed of 4 distinct nutlets, enclosed within the tube of the persistent calyx; nutlets ovoid, up to 1.25 mm × 1 mm, black; in water the nutlet-wall produces a thick white cover of slimy threads within several minutes.
- Seed free within the nutlet.
Growth and development
Seeds normally germinate within 1-2 weeks after sowing. Germination is epigeal. Flowering starts 8-12 weeks after sowing, when plants are about 25 cm tall and continues until the plants die, but data differ considerably with cultivar. Insect pollination is normal, causing cross- and self-pollination. Seed maturation takes 14-20 weeks from sowing. In the wild, flowering and fruiting occurs year-round.
Other botanical information
Within the genus Ocimum L., species delimitation is far from being clear. Here the view expressed in Flora Malesiana is being followed, where 4 species for Malesia are distinguished (O. americanum, O. basilicum, O. gratissimum and O. tenuiflorum), but differences are small and many hybrids seem to exist. O. americanum could well be a diploid form (2n= 24) of the tetraploid (2n= 48) O. basilicum. For the cultivated Ocimums, recognition of one taxon O. basilicum, subdivided into cultivar groups and cultivars might give a solution, but first a thorough revision of the genus is needed.
Hoary basil is often found growing on roadsides, in fields, in teak forests, and in open waste places close to settlements. It prefers sunny, wind-sheltered spots. It grows well from the plains up to 500(-2000) m altitude, preferably on upland soils, but it is also planted on dikelets of paddy fields.
Hoary basil is extensively cultivated in home gardens in Indonesia and Malaysia, but also in commercial market gardens near the large urban centres. It is propagated by seed, usually sown in a seed-bed, and transplanted 3-4 weeks later on beds at planting distances of 20-30 cm either way. Weed control is important, especially because weeds can ruin the quality if they are included in the harvested crop.
No serious diseases and pests have been reported. Harvesting starts about 2-3 months after planting, and is done subsequently at regular intervals. Harvesting usually consists of cutting young shoots about 10 cm long, but cutting back the whole plant is also practised, as well as once-over harvest by uprooting. Plants selected for seed production are not pruned. Seeds are harvested by cutting dry inflorescences, which are sun-dried and threshed by beating.
Genetic resources and breeding
Germplasm collection of Ocimum spp. by the Centre for Research and Development in Biology, Bogor, Indonesia, showed that O. americanum and O. tenuiflorum are the most common species in Indonesia. The O. americanum samples showed considerable variation in stem and flower colour, leaf structure, leaf scent and taste.
Selection and breeding work has not been undertaken in the South-East Asian region. Interspecific hybrids with O. basilicum are easily obtained, but they show strongly reduced pollen fertility.
Although there is considerable information on Ocimum spp., it can often hardly be used because of a lack of clarity about the taxonomical identity of the material studied. The priority in Ocimum research is to unambiguously establish a link between taxonomical and non-taxonomical information.
- Boonklinkajorn, P. & Chomchalow, N., 1968. Preliminary study of the effect of plant density on the yield of Ocimum spp. Thailand Institute of Scientific and Technological Research (TISTR), Bangkok, Thailand. Research Project No 11/18. Technical Report No 3. 18 pp.
- Darrah, H.H., 1974. Investigation of the cultivars of the basils (Ocimum). Economic Botany 28(1): 63-67.
- Keng, H., 1978. Labiatae. Ocimum. In: van Steenis, C.G.G.J. et al. (Editors), 1950- . Flora Malesiana. Series 1. Vol. 8. Sijthoff & Noordhoff International Publishers, Alphen aan den Rijn, the Netherlands. pp. 376-379.
- Lubis, S.H.A., Murni Dwiati & Prana, T.K., 1986. Collection of Ocimum spp. in Indonesia. IBPGR/RECSEA Newsletter 10(2): 8-10.
- A.T. Sunarto