Abstract: Root pressure constitutes a fundamental hydraulic force that facilitates the upward transport of water and dissolved nutrients through the vascular system of plants. Studying the relationships among root pressure, root traits, and plant height provides critical insight into the mechanisms underpinning plant growth. Unlike terrestrial plants, aquatic species typically experience minimal water deficiencies, suggesting that their root pressure regulation may operate through distinct physiological pathways influenced by environmental variables such as temperature and light. To investigate these dynamics, the association between root pressure, root traits, and plant height was examined in the aquatic invasive species Myriophyllum aquaticum. Results showed that: (1) Root pressure was first detected on the fourth day following the planting of cuttings; (2) The timing of peak root pressure in M. aquaticum differed significantly, occurring between 0:00 and 2:00 a.m., whereas in terrestrial plants, the peak typically occurred between 0:00 and 5:00 a.m.; (3) Root pressure exhibited a significant positive correlation with root morphological traits and was detectable only after roots exceeded a certain threshold, characterized by a maximum root length of approximately 20.23 mm, beyond which pressure increased significantly; (4) Unlike terrestrial plant species such as bamboo, root pressure did not serve as the primary factor constraining plant height in M. aquaticum. These results suggest that although the relationship between root pressure and root development in M. aquaticum parallels that of terrestrial plants, the mechanisms governing vertical growth differ under aquatic conditions.