We report, for the first time, shape-tuned and sizetuned synthesis of silver nanoparticles using extracts of the weed lantana (Lantana camara). The purity, crystal structure and possible biomolecules responsible for the nanoparticle formation were explored with SEM, Hr-SEM, TEM, EDAX, XRD, zetasizer and FTIR techniques. The distinguishing feature of the present study is that it enables the fabrication of silver nanoparticles with a non-hazardous, energy-saving, and cost effective method. Simultaneously the study enables gainful utilization of an obnoxious invasive weed, which is otherwise not only worthless but also seriously harmful to the environment.