Parasitism (GK. Para-beside, sitos-food) is a close association between two living organisms of different species where one is benefitted (called parasite) and the other is harmed (called host). In parasitic mode of nutrition, the parasites obtain their nutrition from the host tissue by special structure called haustoria. Haustoria are metabolically very active and exihibit enzymatic activity. Parasitic plants are either total or partial parasites and they may be stem or root parasites.