importance of plants as a drug source

Since ancient time mankind depended on plants as a remedy for their illness.At that times people or even the physician doesn't know about the constituents in that particular plant.The major reason for that is that the knowledge they had is simply trasmitted from generation to generation and they are simply using it.For example ayurveda, the ancient system of medicine in india.In this majority of drugs used are crude plants.
As time progressed,the search for new molecules resulted in screening of plants and which resulted in isolation of new lead compounds.And these compounds provide outstanding contribution to modern therapuetics.Examples for such discoveries include isolation of serpentine from roots of Rauwolfia serpentina in 1953.Similarly isolation of vincristine and vinblastine from Catharanthus roseus revolutionised the cancer therapy.These are a very few examples of plants that contributing to therapuetics.
So these examples clearly indicate the importance of plants.So it is very important to screen those plants that are using in indigenous systems of medicine
Their is doubt that many asian,african and latin american countries have unexplored source of medicinal plants.Screening of such plants will obviously provide some lead compounds and that offer cure to many disease like cancer,AIDS etc.
One of the consistent challenges in screening of such plants is the incorporation from the peoples especially tribes using these plants.The WHO should take necessary measures on this matter.
There is no doubt in the importance of plants in future therapeutics.Plants will serve the humanity by providing lead compounds.