Regional Variability in Growth and Leaf Functional Traits of Mitragyna speciosa in Thailand

Kratom (Mitragyna speciosa (Korth.) Havil.) is a tropical evergreen species native to Southeast Asia, widely recognized for its medicinal properties. Recent legal changes in Thailand permitting its cultivation and commercial use have increased interest in understanding the optimal conditions for its growth, particularly in regions beyond its native southern habitat. This study examined the leaf functional traits associated with kratom’s growth in the southern (native habitat), central, and northeastern regions of Thailand. Species adaptation was determined by analyzing variations in leaf functional traits across different environments. The results showed that the specific leaf area (SLA), leaf thickness, chlorophyll content (SPAD), and stomatal density (SD) did not exhibit any significant regional variations. However, the leaf pH, performance index (PI), and quantum yield (Fv/Fm) differed significantly across regions. The northeastern region had higher leaf pH and lower photosynthetic efficiency compared to the southern and central regions. Non-Metric Multidimensional Scaling (NMDS) ordination indicated that environmental factors such as elevation, light intensity, temperature, and soil water content significantly influenced leaf trait variability in the northeastern region. These findings demonstrate kratom’s ability to grow under diverse environmental conditions, potentially indicative of cultivation beyond its native range.