The green and selective synthesis of triangular nanoplates (NPs) is shown to arise out of the slow rate of reduction and generation of Au(0) from HAuCl4. Toward this purpose, the small molecules present along with the polysaccharide in bael gum (BG) are separated; their structures are identified, and their role in the reduction of HAuCl4 in aqueous solution as well as their possible role in shape direction are studied. The observations suggest that in all the cases studied the slow rate of reduction could be the primary reason for shape selectivity toward formation of NPs, and the role of small molecules is possibly limited to that of a reducing agent. This was further confirmed by carrying out the reduction reaction in some detail by using imperatorin oxide (one of the molecules isolated from BG) at different concentrations. At higher concentrations of imperatorin oxide, the formation of pseudospherical and rodlike particles (instead of smaller NPs) in solution further confirmed the hypothesis. The formation of pseudospherical Au nanoparticles from BG, at high concentration and ambient temperature or relatively lower concentration and high temperature, as well as the formation of NPs from purified BG at ambient temperature reinforce the hypothesis that a moderate reduction rate results in the formation of triangular Au NPs. © 2017 American Chemical Society.