The present study investigated the palynological diversity of highly medicinal Rare, Endangered, and Threatened (RET) plant species dwelling in higher altitudes of Western Himalaya, India. The pollen morphology of 32 plant species covering 29 genera, 23 families, and 18 orders of Angiosperms was analyzed by Light Microscopy (LM) and Scanning Electron Microscopy (SEM). The families of the studied plant species have been arranged and discussed following the evolutionary sequence as per the updated version of Angiosperm Phylogeny Group ІV. The studied pollen characters were found to be helpful in the delimitation of taxa at the species level. In the studied monocots, the species belonging to order Zingiberales, Asparagales, and Liliales followed the general trend of having primitive inaperturate to advance monosulcate pollen except for Alismatales which had inaperturate pollen and placed after the orders mentioned above in the APG ІV classification system. The pollen aperture of the eudicot group in the present study followed the evolutionary pattern from tricolpate to tricolporate and triporate, which corroborated previous reports. All the investigated species of both monocot and eudicot groups had monad pollen units suggesting their primitiveness on the evolutionary scale except for the Rhododendron companulatum (Ericales), having evolutionarily advanced tetrad arrangement. The current study found primitive exine ornamentation in Ranunculales to advance in Asterales, Lamiales, Gentianales, and Boraginales and confirms the results of the previous studies. The data on the pollen morphological features of the studied species generated in the present study will help understand these important high-altitude plant species' reproductive biology and conservation aspects. © Articles by the authors; Licensee UASVM and SHST, Cluj-Napoca, Romania. The journal allows the author(s) to hold the copyright/to retain publishing rights without restriction.
