Comparative Analysis of Pollen Morphological Traits in Halophytic Chenopods

Background and Objective: Halophytic plants exhibit various adaptive mechanisms to survive in high-salinity environments, one of which involves modifications in pollen morphology and internal tissues. However, limited information exists on the pollen traits of halophytes in saline habitats. This study aims to investigate the pollen morphological characteristics of halophytic species within the family Chenopodiaceae to understand their potential adaptive significance and evolutionary relationships. Materials and Methods: Pollen grains of 16 halophytic species belonging to 10 genera of Chenopodiaceae were collected from salt marsh habitats along the Western Coastal Region of Egypt, spanning from Alexandria to Mersa Matrouh, between October, 2018 and April, 2020. Pollen samples were prepared using acetolysis for light microscope examination; non-acetolysed pollen was sputter-coated with gold for scanning electron microscope investigation. Morphometric data, including pollen diameter and number of pores per pollen, were recorded and analyzed descriptively. Results: The study revealed notable variation in pollen diameter and number of pores per pollen grain, ranging from 12 to 62 pores. All studied species shared common features: Symmetric, apolar, spheroidal, zonopantoporate pollen grains with ornamented pores and a tectate imperforate exine. The exine was generally thin to moderately thick, with granulate or echinate surface textures. Based on pollen diameter, species were grouped into three categories: (1) Small grains 20 μm (e.g., Salsola longifolia, S. tetragona, S. volkanesii, (2) Medium grains 20-30 μm (e.g., Atriplex halimus, Anabasis articulate, Chenopodium album, and Chenopodium murale, and (3) Large grains 30 μm, including obligate halophytes and Basia muricata. Each group was further subdivided according to pore number: <20, 20-40, and>50 pores per pollen grain. Conclusion: The presence of small, pantoporate pollen grains with thin exine layers among these halophytic Chenopodiaceae species suggests a common evolutionary origin and possible adaptive modifications to salinity stress. These morphological features may contribute to their reproductive success in a saline environment and offer insights into phylogenetic relationships within the group.