We report, for the first time, shape-tuned and size-tuned 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.