The aim of the study was to analyze the growth and development of two species of duckweed: Lemna minor and Lemna trisulca under different combinations of temperature (15-25°C) and photoperiod (12-24 hours), while controlling physicochemical parameters such as electrical conductivity, pH, and oxygen content. The plants were placed in synthetic nitrogen medium, and their growth was monitored for 40 days. Statistical methods, including analysis of variance (ANOVA) and principal component analysis (PCA), were used for data analysis. The results showed that both species grow better at higher temperatures (25°C) and longer photoperiods (24 hours). Lemna minor achieved higher surface coverage (up to 58.4%) and biomass (over 1.44 g fresh weight) under optimal conditions (25°C and a 12-hour photoperiod), indicating its high efficiency in utilizing favourable conditions. Lemna trisulca, on the other hand, showed a more stable increase in biomass (1.03 g fresh weight) and cover (45.8%) under its extreme conditions (15°C and 12- hour photoperiod). Regarding adaptation to changing physicochemical conditions, Lemna minor responded better to favourable parameters, achieving higher growth rates under optimal pH (6.05) and electrical conductivity (31,6 µS/cm), while Lemna trisulca showed stable growth even in more variable conditions, with minimal decrease in growth under higher conductivity (583 µS/cm) and lower pH (6.96). The research findings reveal that Lemna minor is more competitive under optimal conditions, which may result from its more efficient use of available resources. Its rapid growth makes it particularly valuable in bioremediation, while Lemna trisulca may cope better with variable aquatic conditions. The conclusions emphasize the adaptive differences between the two species, which is significant for managing aquatic ecosystems. Lemna minor is suitable for stable environments, whereas Lemna trisulca finds applications in more variable conditions, indicating their diverse potential uses in environmental protection and bioremediation. These studies provide important data on the adaptive capabilities of duckweed, which is essential for effective management of aquatic ecosystems.