Holy basil (Ocimum tenuiflorum) is an aromatic plant in the family Lamiaceae which is native throughout the Old World tropics and widespread as a cultivated plant and an escaped weed. It is an erect, much branched subshrub 30-60cm (1-2ft) tall with hairy stems and simple opposite green leaves that are strongly scented. Leaves have petioles, and are ovate, up to 5cm (2in) long, usually slightly toothed. Flowers are purplish in elongate racemes in close whorls. There are two main morphotypes cultivated in India—green-leaved (Sri or Lakshmi tulsi) and purple-leaved (Krishna tulsi).
There is also a variety of Ocimum tenuiflorum which is used in Thai cuisine, and is referred to as Thai holy basil, not be confused with Thai basil, which is a variety of Ocimum basilicum.