Recently, the exploitation of biological systems has emerged as a novel technique for the synthesis of nanoparticles. There is a growing need to develop clean, non-toxic and environment friendly procedures (‘green chemistry’) for synthesis and assembly of nanoparticles. We have been studying various crops to determine their potential to synthesize nanoparticles. We report that alfalfa and other crops have ability to remove potassium tetrachloroaurate (gold III ions), and transform gold (III) ions into a large quantity of gold nanoparticles. Electron microscopy revealed the intracellular distribution of monodisperse nanospheres, possibly due to reduction of the metal ions in cells. X-ray absorption near-edge structure and extended X-ray absorption fine structure demonstrated a high degree of efficiency for the biotransformation of Au(III) into Au(0) by plant tissues.