<p>Cadmium (Cd) contamination threatens aquatic ecosystems and human health. Duckweeds are ideal for toxicological studies due to their rapid growth and high metal uptake. While interactions between single duckweed species and Cd has been extensively studied, the impact of duckweed diversity on Cd tolerance remains unknown. This study examines three duckweed species (<i>Lemna minor</i>, <i>Landoltia punctata</i>, and <i>Spirodela polyrhiza</i>) under Cd stress, assessing growth, chlorophyll content, Cd accumulation, removal efficiency, and metabolic adaptations in monoculture and mixed-culture systems. The results showed that the growth of duckweeds was inhibited across all cultivation modes under 10 mg L⁻¹ Cd stress, with growth rates remaining below 0.1 g d⁻¹ and experiencing more than 80% inhibition. Moreover, chlorophyll content declined with increasing Cd concentration under all cultivation modes, exceeding 64% inhibition under 10 mg L⁻¹ Cd stress. Cd accumulation peaked in <i>L. minor</i> monoculture at 10 mg L⁻¹ Cd (1601.33 mg kg⁻¹), with bioenrichment coefficients exceeding 50 in all systems. The combination of <i>S. polyrhiza</i> and <i>L. minor</i> exhibited the highest Cd removal efficiency, achieving 50.60% at a Cd concentration of 1 mg L⁻¹. However, the Cd removal rate of all culture modes was below 30% when the Cd concentration increased to 10 mg L⁻¹. Elevated antioxidant enzyme activities (POD, CAT) and malondialdehyde (MDA) levels indicated enhanced oxidative stress responses. This study provides support for the application of duckweed polycultures in water contaminated with heavy metals.</p>