There are over 400 different tribal and other ethnic groups in India. The tribals constitute about 7.5 per cent of Indian population (Gupta, 1970). Apart from the tribal groups, many other forest dwellers and rural people also possess unique knowledge about plants. Tree worship played an important role in the religious history of India. The plants form the oldest association with human dwelling and ancient Indian cultures flourished in the midst of dense forests. They are offered in worship to several deities and different species are associated with different Gods. Some important plants like Ocimum sanctum L. (Tulsi), Aegle marmelos L. (Bel) and Musa sapientum L. (Kardali) which are important in folk religion and also worshipped as symbols of Gods and Goddesses (Altschul, 1973). Records of early civilization in all parts of the world reveal that a considerable number of drugs used in modern medicine were in use even in ancient times. The use of plants for curing various human ailments figured in ancient manuscripts such as The Bible, The Rig-Vedas, The Iliad and The Odyssey and the History of Herodotus. Over 6000 years ago, the ancient Chinese were using drug plants. The Egyptians, Babylonians, Sumerians, Greeks and Romans, all developed their respective characteristic Materia Medica. On the other side of the world, the Aztecs, Mayans and Incas had all developed primitive medicine. Some of the ancient Egyptian text books “papyri” (such as the Edwin Smith Papyrus and the Ebers Papyrus), written as early as 1600 B.C., indicate that the Egyptians had an amazingly complex Materia Medica. Apart from the names of many medicinal plants then known, the papyri also included several hundreds recipes or prescriptions for various diseases. The Edwin Smith Papyrus (about 1750 B.C.) is now one of the prized collections of the New York Academy of Medicine. In India, the Ayurvedic system of medicine has been in use for over 3000 years. Charaka and Susruta, two of the earliest Indian authors had sufficient knowledge of the properties of the Indian medicinal plants. Their medical works, the Charaka Samhita and the Susruta Samhita are esteemed even today as treasures of literature on indigenous medicine. Charaka was the contemporary of Sushruta who wrote a book on medicines entitled Charaka Samhita. These two are the treasures of literature on Ayurvedic medicine (Jain, 1968 and Mitra and Jain, 1991). Among the ancient civilization, India has been known to be a rich repository of medicinal plants. The Rigveda (5,000BC) mentioned 67 medicinal plants, the Yajurveda 81 and the Artharvaveda (4500-2500 BC), 290 species. Charak Samhita (700 BC) and the Sushruta Samhita (200BC) described the properties and uses of 1,100 and 1,270 plants respectively in compounding of drugs and these are still used in classical formulation in the Ayurvedic system of medicine. The classical medical systems such as Ayurveda of India lean heavily on natural products. In India, 1250-1400 species are recognized for providing raw materials for Ayurvedic formulations (Dev, 1999) and 342 species and 328 species are recognized to provide raw material for Unani and Siddha formulations respectively (Shiva, 1996). Ayurveda, the foundation stone of ancient medical science uses plants and herbs not only to cure disease but also to provide a source of minerals and vitamins which give proper health and nutrition to human being (Fransworth, 1990). The rasayana therapy of Ayurveda generally consists of rejuvenating and nourishing drugs for longevity, memory enhancement, immunomodulation and adaptability. Patwardhan (2000) has considered it to be an innovative source of immunodrugs. There is a vast data on medicinal plants of India, not only in the ancient time like the Rig-Vedas, Samhita, the Nighantus and in text books of Ayurveda, Unani and Siddha system but in other publications of modern times viz. of nineteenth and twentieth centuries. Jain (1987) and Mitra and Jain (1991) have recently reviewed this work. According to current estimates nearly three fourth of the drugs used for curing human ailments in India are of plant origin (Mitra and Jain, 1991). Plants provide the predominant ingredients of medicines in most medical tradition. Estimates for the number of species used medicinally include: 35000-70000 worldwide (Fransworth and Soejarto, 1991), 10000-11250 in China (Xiao and Yong, 1998 and Pei, 2002), 7500 in India (Shiva, 1996), 2237 in Mexico (Toledo, 1995) and 2572 traditionally by North American Indians (Moerman, 1998). India and China are the world’s leading producing nations of medicinal and aromatic plants (Rao et al., 2004). The Greeks and Romans were familiar with many of the present day drugs as is evident from the work of Hippocrates(460-370B.C.), Aristotle (384-322 B.C.), Theophrastus (370-287 B.C.), Pliny the Elder (A.D.23-79), Dioscorides (A.D.50-100) and Galen (A.D.131-201). They wrote extensively about medicinal herbs, giving their names along with a description of each plant, illustrations, their putative healing properties and also complex descriptions for the preparation of medicines. Hippocrates, the ‘Father of Medicine’, was the first to attempt a scientific explanation for diseases. His influence remains today in the Hippocratic oath taken by young doctors upon their graduation from medical school. Dioscorides, treatise on medicinal plants De Materia Medica remained the supreme authority for over sixteen centuries, during which the manuscript was laboriously copied and recopied with few additions. In like manner, the works of Aristotle, Galen and even Pliny were copied and handed down with increasing inaccuracies. During the Dark Ages (A.D. 400-1000) few new ideas were added. During the Middle Ages (A.D. 1000-1500) also little significant botanical progress was made.