<p>Plant-based green synthesis of metal nanoparticles offers a biodegradable, environmentally friendly alternative to traditional chemical and physical processes, using phytochemicals as natural reducing and stabilizing agents. This review is particularly on four highly researched metallic nanoparticles—gold (AuNPs), silver (AgNPs), zinc (ZnNPs), and copper (CuNPs)—prepared from plant extracts. We review major synthesis methods, emphasize the role of bioactive metabolites in stabilization and nucleation, and contrast characterization techniques, including DLS, TEM, AFM, and XRD, for analyzing size, morphology, and stability. In addition to synthesis, we critically examine environmental and biomedical applications such as antimicrobial, antioxidant, anticancer, and remediation purposes, and describe existing challenges like reproducibility, scalability, and standardization of protocols. Through the integration of mechanistic understanding with comparative analysis, this review highlights the promise of metallic nanoparticles from plant sources and sets out directions for future research to extend laboratory promise to industrial translation.</p> Graphical abstract <p></p>