<p>The present investigation aims at assessing the allelopathic potential of <i>Alternanthera ficoidea</i>, an alien invasive weed in West Bengal, India. The allelopathic efficacy of leaf extracts in both aqueous and organic solvents of <i>A. ficoidea</i> has been evaluated from changes of germination and metabolism analyses of mung bean [<i>Vigna radiata</i> (L.) R. Wilczek K-75] seeds. The extracts altered the germination behaviour, recorded in terms of percentage, <i>T</i>₅₀ values, speed, and TTC stainability of germinating seeds. The contents of insoluble carbohydrates, proteins, DNA and RNA as well as activities of catalase and dehydrogenase in seed kernels have been reduced. In contrast, the levels of amino acids, soluble carbohydrates, and amylase activity have been found higher in treated seeds. Reduced germinability and metabolism were fully concentration dependent. Chromatographic separation and HPLC purification followed by HRMS of methanolic leaf extract of <i>A. ficoidea</i> have resulted in identifying six putative allelochemicals with carboxylic acid functionality. These include: 4-(Hexyloxy)benzoic acid (<b>1</b>), α-Linolenic acid (<b>2</b>), 13-Hydroxy-9,11 octadecadienoic acid (<b>3</b>), 4- Coumaroylquinic acid (<b>4</b>), 2-methyl 13-docosenoic acid (<b>5</b>), and 3-(4-Diethylamino-2-hydroxyphenylazo)-4-hydroxybenzenesulfonic acid (<b>6</b>). The cumulative impact of these allelochemicals reflected on regulation of germination and metabolism of mung bean seeds, including germination percentage, <i>T</i>₅₀ values, and speed of germination. The allelopathic potential of <i>A. ficoidea</i> on the mung bean seeds has further been elucidated using steady-state fluorescence spectroscopy.</p>