Pollen Morphology and Taxonomic Significance of Current (Thurya capitata and Nephelochloa orientalis) and Former (Aegokeras caespitosa) Monotypic Endemic Taxa of Türkiye

This study investigates, for the first time, the detailed pollen morphology of three endemic taxa of Türkiye associated with monotypic or historically monotypic lineages: Thurya capitata Boiss. & Balansa (Caryophyllaceae), Nephelochloa orientalis Boiss. (Poaceae), and Aegokeras caespitosa (Sibth. & Sm.) Raf. (Apiaceae), and evaluates the taxonomic significance of their pollen characters. Pollen grains prepared using the Wodehouse method were examined by light and scanning electron microscopy. Thurya capitata has monad, prolate-spheroidal (polar axis/equatorial axis ratio, P/E = 1.01), polypantoporate pollen with 6–9 pores and microechinate-perforate exine ornamentation. Aegokeras caespitosa has monad, prolate (P/E = 1.9), tricolporate pollen with rugulate ornamentation; its most distinctive feature is the very long and narrow colpus. Nephelochloa orientalis has prolate-spheroidal (P/E = 1.01), annulate-monoporate pollen with microechinate-areolate ornamentation, while occasional diporate forms were also observed. Quantitative measurements further differentiated the taxa in pollen size, aperture dimensions, and wall thickness. Among the examined taxa, T. capitata had the largest pollen grains, whereas A. caespitosa showed the most elongated pollen form. The observed characters are consistent with the general pollen features of their respective families while also revealing diagnostic differences among the taxa. These data provide useful palynological information for evaluating their taxonomic and systematic relationships within their respective families and may contribute to future comparative studies of endemic taxa of Türkiye.