Stem adaptation in Heteranthera zosterifolia Mart. (Pontederiaceae) across distinct water depths

A significant correlation between water level fluctuations and morphological traits in macrophytes is well-documented, especially in shallow water species. However, predicting morpho-anatomical characteristics in submerged plants across water depths remains challenging. We investigated morpho-anatomical variations in Heteranthera zosterifolia stems from a deep flooded doline at three depths: surface, 2.5m, and 5m. The anatomical survey followed standard protocols, and variance analysis was used based on the measurements obtained. Our study revealed significant differences in the stem and aerenchyma area, number of air channels, cortex thickness, stele-cortex ratio, and average vessel diameter between surface specimens and those from greater depths. The anatomical survey highlighted a greater investment in the cortex and aerenchyma area in water surface specimens, potentially related to structural stability and buoyancy. This challenges the conventional belief that deeper water increases the stem’s area and number of air channels, questioning the traditional association of aerenchyma solely with oxygen transport. Moreover, a balance in vessel diameter between surface and deeper specimens suggests considerations for transport efficiency, protection against water stress, and buoyancy needs. The morpho-anatomical adaptation of the H. zosterifolia stem yields significant implications for the strategies employed by the species for survival and growth in deep aquatic environments.

Keywords:
Aerenchyma; aquatic macrophytes; flooded doline; hydrophytes; Poales; Pontederiaceae; stem anatomy