Invasive species are emerging as one of the major threats to sustainable development, on par with global warming and destruction of life–support systems. These alien species come in the form of plants, animals and microbes that have been introduced into an area from other parts of the world, and have been able to displace the indigenous species (Preston and Williams, 2003). The invasive species are widely distributed among all categories of living organisms as well as all kinds of ecosystems throughout the world (Hobbs and Humphries, 1995). Convention on Biodiversity (CBD, 2010) visualized that invasion by the exotic species is one of the leading threat to native wildlife. Several characteristics of the species help them to be invasive. Most important among them are the large quantity of seeds they produce which are mostly very small so as to be carried away to long distances by wind and water (Khare, 1980; Enserink, 1999). Many invasive plants produce allelochemicals which halt the