<p>Green, plant-mediated synthesis of boron-containing nanomaterials is promoted as a safer, more sustainable alternative to conventional high-temperature, solvent-intensive routes, with potential benefits for nanomedicine and environmental safety. This review aims to systematically map green, plant-mediated synthesis routes for boron-containing nanomaterials and to assess their reported medical and environmental implications. A PRISMA-guided literature search was conducted in PubMed, Scopus, Web of Science, and Google Scholar from 2017 to 2025. Predefined inclusion and exclusion criteria were applied. For each eligible study, data were extracted on nanomaterial type, biological source (plant or microbe), synthesis conditions, characterization, biomedical application, and ecotoxicological outcomes. Evidence for green synthesis was found mainly for boron-doped metal oxides and a limited number of bio-assisted boron nitride systems, which showed antimicrobial, photocatalytic, anticancer, or plant-stimulatory effects at optimized doses. No genuinely plant-mediated routes were identified for carboranes, metallacarboranes, or other high-boron-density clusters, despite their central role as BNCT carriers. Environmental and toxicological data were scarce but generally indicated low to moderate toxicity at realistic exposure levels, with adverse effects emerging predominantly at high concentrations. Plant-mediated synthesis already offers promising routes for selected boron nanomaterials, but it has not yet been extended to the most clinically relevant boron clusters. Bridging this gap will require new bio-inspired synthetic strategies, standardized characterization, and long-term environmental studies.</p> Graphical Abstract <p></p>