1.1 The Plants Role in Human
Medicinal plants have always been associated with cultural behaviours and traditional knowledge. The renaissance of interest in plant products has been stimulated by the use of plant extracts in chronic conditions for which conventional drugs is perceived to offer very little specificity in its target (Rhiouani et al., 1999). This has resulted in the use of large number of medicinal plants with curative properties to treat various diseases (Verpoorte, 1998). Nearly 80% of the world‘s population relies on traditional medicines for primary health care, most of which involve the use of plant extracts (Akindele and Adeyemi, 2007).
The blind dependence on synthetics is over and people are returning to the naturals with hope of safety and security. Also, the development of adverse effects and high microbial resistance to the chemically synthesized drugs, has forced men into ethnopharmacognosy. More so, in our local situation, degree of ignorance and illiteracy had forced many to abandon or neglect pharmaceutically formulated drugs in favour of locally prepared herbal remedies coupled with the fact that pharmaceutical products are increasingly being faked. Thus, the herbal products today symbolise safety in contrast to the synthetics that are regarded as unsafe to human and environment (Joy et al., 2001). Herbs are staging a comeback, herbal ‗renaissance‘ is happening all over the globe and people returning to the naturals with hope of safety and security. By and large, the public is gradually drifting towards acceptance and usage of herbal preparations.
In Africa, traditional healers and remedies made from plants play important role in the health of millions of people (Adotey et al., 2012). The users of these remedies, found literally thousands of phytochemicals from plants as safe and broadly effective alternatives with less adverse effects. The Pharmacognosy Society of Nigeria supports the acceptance of herbal remedies or treatment of ethnomedicinal practice along with conventional orthodox health care system (Ndukwe, 2004). This is largely due to the fact that plants used for traditional medicine contain a wide range of substances that can be used to treat chronic as well as infectious diseases (Duraipandiyan et al., 2006).
Biological organisms particularly plants produce two distinctly different types of chemical products. The first type, primary metabolites, which consists of compounds such as sugars and proteins that are common to most organisms and are essential for functional metabolism. Secondary metabolites, on the other hand, are chemicals unique to a single species or related group of organisms. Not until the 1990s that scientists fully realize that these secondary metabolites are more than mere leftovers from an organisms metabolic processes. These chemicals can function as communications tools, defense mechanisms or sensory devices. The biological activity of these chemicals is beneficial to the organism that produces them, but it is often harmful to other species, including humans (Swerdlow, 2000). This toxicity can adversely affect the functions of the entire human body or only a specific biological process, such as the growth of cancer cells (Yoder, 2005). Also, many beneficial biological activity such as anticancer, antimicrobial, antioxidant, antidiarrheal, analgesic and wound healing activity of plants have been reported. In this way, certain foreign, naturally produced chemicals can act as powerful drugs when administered at the proper concentration (Yoder, 2005).