Elevation-driven morpho-anatomical adaptations in Withania coagulans (Stocks) Dunal from the Koh-e-Suleiman highlands

Elevational gradients form highly effective environmental filters which determine the morphological and internal pathways of plants, leading to adaptive changes in natural populations. Withania coagulans (Stocks) Dunal is an ecologically and medicinally valuable species commonly growing throughout the Koh-e-Suleiman Highlands of Pakistan, but its altitude-associated adaptive compensations are not well understood. This paper examined morphological and anatomical diversity in the populations of W. coagulans that varied in terms of altitudes with an aim of explaining structural adaptations in the face of environmental differences. Morphological parameters such as root length, plant height, leaf area, and number of leaves per branch had high site-specific variance, with maximum growth performance observed in the Lundi Saidan population and minimum growth performance seen in the Fort Munro Road population due to variation in environmental constraints in terms of altitude and temperature. Root anatomical characteristics, including epiblema thickness, cortical thickness, metaxylem area, endodermal thickness, and root radius, exhibited different patterns of adaptations with respect to efficiency of water uptake and ionic regulation. Stem structural characteristics brought about a variation in epidermal thickness, cortical thickness, vascular tissue, pith area, and stem radius as evidence of mechanical support and internal water storage. Further functional adaptations that were not previously mentioned regarding transpiration regulation and hydraulic conductivity were also revealed by leaf anatomical characteristics such as epidermal thickness, midrib thickness, vascular bundle area, metaxylem area, and stomatal density. The presence of both morphological and anatomical responses suggests a high level of phenotypic plasticity of W. coagulans, which allows populations to maximize growth, regulate water relations, and hence, tolerance to stress conditions along elevation gradients. These results provide new information about the adaptive structural solutions to highland medicinal flora and provide a scientific foundation for conservation planning and habitat-specific culture of W. coagulans in mountainous areas.