Comparative Analysis of the Morphological and Anatomical Characteristics of Populus L. (Salicaceae Mirb.) Species in the West Kazakhstan Region of Kazakhstan

The genus Populus L. includes ecologically important woody species that occupy diverse floodplain habitats and exhibit considerable morphological and anatomical variation. The aim of this study was to comparatively assess the morphological, anatomical, and dendrometric characteristics of four Populus taxa-P. alba, P. nigra, P. tremula, and P. × canescens-growing in different floodplain habitats of the West Kazakhstan region. Leaf and stem samples were collected during 2025–2026 and examined using conventional anatomical techniques. Quantitative measurements were performed for epidermal, cortical, vascular, and mesophyll tissues, as well as for leaf and tree morphological characteristics. Statistical analyses were conducted in R using descriptive statistics, correlation analysis, and principal component analysis (PCA). The results revealed pronounced interspecific differences in both anatomical and morphological traits. P. alba was characterized by the largest leaf dimensions and the highest dendrometric values, with mean leaf length, width, and petiole length of 9.37 ± 1.63, 7.83 ± 1.29, and 7.41 ± 1.56 cm, respectively, while mean tree height, crown radius, and trunk diameter reached 134.41 ± 57.81, 21.38 ± 9.20, and 42.77 ± 18.41, respectively. P. nigra was distinguished by the largest central cylinder diameter (1085.7 ± 123.2 μm), the thickest xylem (50.7 ± 6.9 μm), and the presence of calcium oxalate crystals in the primary cortex and pith. P. tremula showed the thickest primary cortex (307.8 ± 9.7 μm), whereas P. × canescens had the smallest central cylinder (228.0 ± 45.0 μm) and generally lower dimensions of vascular tissues. Correlation analysis demonstrated strong positive relationships among leaf traits and among dendrometric traits, while leaf and dendrometric characteristics showed predominantly negative relationships at the interspecific level. PCA based on leaf traits explained 93.6% of the total variation in the first two components, whereas the integrated PCA of six leaf and dendrometric traits explained 97.0%. P. alba formed the most distinct morphological group, while P. tremula and P. × canescens showed substantial overlap, reflecting their close morphological similarity and the hybrid origin of P. × canescens. The combined application of anatomical, morphometric, dendrometric, and multivariate approaches provides effective diagnostic criteria for differentiating closely related Populus taxa and contributes to a better understanding of their structural diversity and ecological adaptation in the floodplain ecosystems of Western Kazakhstan.