Comparative Morphology, Palynology and Achene Micromorphology of Tanacetum oxystegium (Sosn.) Grierson and Tanacetum pinnatum Boiss. (Asteraceae) in Türkiye

The genus Tanacetum L. (Asteraceae) exhibits high diversity in Türkiye with 62 taxa, including 27 endemic taxa. This study aims to provide a comprehensive comparative analysis of the morphology, achene and pollen characteristics of Tanacetum oxystegium and T. pinnatum to clarify these features and contribute to the taxonomic boundaries of the species investigated. Plant materials were collected from natural habitats in the Erzurum region in 2024. Macro- and micromorphological investigations were conducted using light microscopy (LM) and scanning electron microscopy (SEM). Results indicated that while both species possess obconical achenes with 5–8 longitudinal ribs and a serrate-dentate corona, they differ significantly in surface ornamentation. T. oxystegium is characterized by striate ornamentation and the presence of slime cells, whereas T. pinnatum exhibits a reticulate-striate surface. Palynological analysis revealed that the two species have radially symmetrical, isopolar and trizonocolporate pollen with echinate-perforate ornamentation. However, T. oxystegium is distinguished by a larger Amb, thicker exine and longer spines compared to T. pinnatum. These findings demonstrate that achene and pollen morphology serve as robust systematic markers for differentiating these morphologically similar taxa and fill a significant gap in the literature regarding their classification.