Introduction
Ocimum L. is a member of the labiatae family. The typical characteristics of this family are square stem, opposite and decussate leaves with many gland dots. The flowers are strongly zygormorphic with two distinct lips. Many of the family, particularly subfamily Neptoideas to which ocimum belongs, are strongly aromatic due to essential oils which consist of monoterpenes, sesquiterpenes and phenylpropanoids.
Ocimum unlike other economically important herbs in the labiatae such as Rosmarinus, thymus and salvia, belongs to tribe ocimae which has declinate stamens.that is stamens lie over the lower[anterior]lip of the corolla rather than ascending under the upper [posterior]lip.
Ocimum was best described by Linnaeus in 1753 who listed five[5] species .Bentham[1832]recognised just under 40 species and divided ocimum into three[3]sections .ocimum [ocymodon benth] with appendiculate posterior stamens;Hierocymum benth with hairs at the base of the posterior stamens and gynmnocium benth with glabrous posterior stamens.The latter two sections contained a few species which are now placed in EndostemonN.E.BR, a genus bentham didn’t recognise or hemizygia. Bentham [1848] then subdivided section section ocimum [ocymodon] into three subsections on the basis of calyx morphology. In subset , ocimum [basilica sensu briquette 1897] the throat of the calyx is open and bearded in subsect. Gratissima the throat is closed by the median lobe of the lower lip,subsection hiantia benth, with truncate lateral calyx lobes, only included species which are sometimes placed in becium [Sebald 1988,1989,paton 1995].Bentham[1848] also added sect ,hemizygia benth. Which briquette [1897] considered to be a separate genus on account of the fused anterior stamens.
Paton [1992] in his revision of African species of ocimum recognised around thirty [30] species and used bentham [1848] infragenic classification of ocimum, with sect hemizygia and subset , hiantia removed, preferring to consider the latter as the separate genus becium. This classification is supported by nutlet characters which bentham did not and by analysis of pollen morphology [Harley et al, 1992]. However this classification is not entirely without problems, as pointed out [Paton 1992] ocimum drdnatum A.J.paton doesn’t fit neatly into the existing categories.ocimum lamiifolium is also anomalous , appearing to have a close relationship to orthosiphon subgenus nautochilus [Bremek.]codd. Pushpangadan [1974,pushpangadan and bradu 1995,sobti and pushpangadan 1979] formulated a different infragenic classification The ‘Basilicum’ group contains herbaceous annuals or sometimes or sometimes perennials with black , ellipsoid, strongly mucilaginous seeds and with a basic chromosome number of n=12 whereas the ‘sanctum’ group are perennial shrubs with brown globose non-mucilaginous or weakly seeds and a basic chromosome number of n=8.the basilicum group contains only section ocimum subsection ocimum.
The remainder of the genus must be placed in the sanctum group. This classification is commonly used in the economic and industrial literature ,e.g barrah[1980], pushpangadan and bradu [1995] whereas bentham system is the basis for that used in taxonomic literature. Economically the most important taxon within ocimum is section ocimum .the most heavily used species are o.basilicum, o.americanum, and their hybrid o x citriodorum. These species are use d for essential oil production and as pot herbs. O.kilmandscharicumis extensively grown in the tropics for camphor production .O.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.
The whole plant and 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 are have laxative properties and are prescribed against gonorrhoea. The essential oil is applied against fever inflammations of the throat. 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 o.gratissimum is used in the ceremonial washing of corpses and is planted in graveyards. In india o.gratissimum named ‘ram tulsi’ is widely used in religious ceremonies and rituals.
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