Pollen morphology and its application in the taxonomy of some species of Tulipa in Iran, Central Asia and Russia

Pollen grains of 30 specimens from different tulip populations of 15 species were studied by light microscope (LM) and for more detailed observations, 13 specimens were studied by scanning electron microscope (SEM). Pollens were collected from living specimens of the Russian Botanical Garden and also from different herbaria of Iran, Central Asia and Russia. In this study, the Acetolysis method was used for LM observations, while for SEM studies, unacetolysis pollen grains were used. The research revealed that the examined species exhibited distinct characteristics, including heterogeneity, bilateral symmetry, monosulcate and trisulcate features, as well as spherical to elliptical shapes. The outline of polar view is spheroidal and equatorial, oblate-spheroidal. They differed from each other in terms of muri and Lumina. The smallest size of pollen grain belonged to T. hoogiana B. Fedtschenko from the subgenus Leiostemones (4.5±2.33 µm), while the largest belonged to T. sylvestris var. biebersteiniana (Schult.f.) Regel) from the subgenus Eriostemone (8.6±4.62 µm). In general, in the subgenus Eriostemones, the pollen grains are monosulcate type, exine ornamentation with perforate-verrucate and reticulate patterns, whereas in the subgenus Leiostemones, there are trisulcate with granulate and psilate ornamentations. Although some of the studied species are considered synonyms using molecular data, their presence in different habitats has caused differences in palynological characteristics. Therefore, palynological characterization of pollen grains can serve as a key trait alongside other characteristics for distinguishing between subgenera, sections, and species in taxonomic studies of the Tulipa.