Myriophyllum aquaticum (M. aquaticum) poses a high invasion risk, yet its heterogeneous ecological adaptation strategies and key environmental drivers remain unclear. This study examined the growth patterns of escaped M. aquaticum populations in a hilly watershed of Sichuan Basin by analyzing plant traits (height, above-/belowground biomass) and environmental factors (seasonality, hydrology, biodiversity, nutrients). Key findings include: 1) The biomass, plant height, and importance value of Myriophyllum aquaticum were significantly greater in aquatic habitats compared to terrestrial habitats. The species exhibited differential adaptation via biomass allocation strategies: in aquatic populations, stolon biomass allocation increased from 40% in winter to 46% in summer, facilitating full spatial occupation of the water column; whereas in terrestrial populations, allocation to stems and leaves increased from 40% to 57%, enhancing competition for light. However, their importance values in summer and autumn remained below 0.5 and declined further as community diversity increased. 2)Season, channel morphology, and species diversity were the primary factors influencing plant trait variation throughout the growing season. M. aquaticum advanced its flowering to March in spring, which promoted rapid biomass accumulation and resulted in a peak biomass of 1.51 kg·m?2 in aquatic habitats by June. In winter, frost damage to apical parts led to a biomass decline to the annual minimum of 0.64 kg·m?2. 3)Hydrological connectivity, by creating stable water levels and nutrient-enriched zones in meandering channels and overflow weirs, significantly increased the biomass and dominance of M. aquaticum, indicating the necessity for targeted management. This study elucidates the invasive mechanism of M. aquaticum via phenotypic plasticity-mediated niche differentiation, offering support for ecological management strategies centered on hydrological connectivity regulation.