Ocimum tenuiflorum (synonym Ocimum sanctum), commonly known as holy basil, tulasi (sometimes spelled thulasi) or tulsi, is an aromatic perennial plant in the family Lamiaceae. It is native to the Indian subcontinent and widespread as a cultivated plant throughout the Southeast Asian tropics.
Tulasi is cultivated for religious and traditional medicine purposes, and for its essential oil. It is widely used as a herbal tea, commonly used in Ayurveda, and has a place within the Vaishnava tradition of Hinduism, in which devotees perform worship involving holy basil plants or leaves.
Holy basil is an erect, many-branched subshrub, 30–60 cm (12–24 in) tall with hairy stems. Leaves are green or purple; they are simple, petioled, with an ovate, up to 5 cm (2.0 in)-long blade which usually has a slightly toothed margin; they are strongly scented and have a decussate phyllotaxy. The purplish flowers are placed in close whorls on elongate racemes .
The three main morphotypes cultivated in India and Nepal are Ram tulsi (the most common type, with broad bright green leaves that are slightly sweet leaves), the less common purplish green-leaved (Krishna tulasi) and the rare wild "vana tulsi". Other less common types of tulsi include a variety called Sri or Lakshmi tulasi, 
Origin and distribution
DNA barcodes of various biogeographical isolates of tulsi from the Indian subcontinent are now available. In a large-scale phylogeographical study of this species conducted using chloroplast genome sequences, a group of researchers from Central University of Punjab, Bathinda, have found that this plant originates from North-Central India. The discovery might suggest the evolution of tulsi is related with the cultural migratory patterns in the Indian subcontinent.
Significance in Hinduism
Tulsi leaves are part in the worship of Vishnu and his avatars, including Krishna and Rama, and other male Vaishnava deities, such as Hanuman. Tulsi is a sacred plant for Hindus and is worshipped as the avatar of Lakshmi. Traditionally, tulsi is planted in the centre of the central courtyard of Hindu houses or may be grown next to Hanuman temples.[full citation needed]
The ritual lighting of lamps each evening during Kartik includes the worship of the tulsi plant, which is held to be auspicious for the home. Vaishnavas traditionally use Hindu prayer beads made from tulsi stems or roots, which are an important symbol of initiation. They have such a strong association with Vaishnavas, that followers of Vishnu are known as "those who bear the tulsi round the neck".
Ayurveda and Siddha
Tulasi (Sanskrit:-Surasa) has been used in Ayurveda and Siddha practices for its supposed treatment of diseases, none of which has been proven by conventional medical research. Traditionally, tulasi is taken as herbal tea, dried powder, fresh leaf or mixed with ghee.
The leaves of holy basil, known as kaphrao in the Thai language (Thai: กะเพรา), are commonly used in Thai cuisine for certain stir-fries and curries such as phat kaphrao (Thai: ผัดกะเพรา) — a stir-fry of Thai holy basil with meats, seafood or, as in khao phat kraphao, with rice. Two different types of holy basil are used in Thailand, a "red" variant which tends to be more pungent, and a "white" version for seafood dishes. Kaphrao should not be confused with horapha (Thai: โหระพา), which is normally known as Thai basil, or with Thai lemon basil (maenglak; Thai: แมงลัก).
For centuries, the dried leaves have been mixed with stored grains to repel insects.
The genome of Tulsi plant has been sequenced and reported as a draft, estimated to be 612 mega bases, with results showing genes for biosynthesis of anthocyanins in Krishna Tulsi, ursolic acid and eugenol in Rama Tulsi.
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