Pollen morphology in Iranian species of Onosma (Boraginaceae)

Abstract

The genus Onosma is one of the largest genera of the family Boraginaceae, with about 240 species distributed mainly in the mountainous habitats of the Irano-Turanian region. Determining the boundaries of the species in this genus has been faced with several problems, and their relationships are still poorly understood based on the recent phylogenetic studies. Therefore, the present study was designed to investigate the pollen micromorphology of 40 species of Iranian Onosma by scanning electron microscopy (SEM), to identify attributes perhaps important for a subgeneric classification. On the basis of pollen SEM images, three types of pollen shapes were observed, and the prolate pollen shape was predominant. In addition, three aperture types were observed. All species studied had microechinate, perforate, microechinate, verrucae, microechinate, perforate, and verrucate, microechinate exine sculpture. Based on cluster analysis and principal component analysis, the species studied were divided into two main groups showing different quantitative and qualitative traits. Therefore, the results of this study suggest that micro-morphological pollen traits can be used as valuable evidence in the taxonomy of the genus Onosma. However, we believe that palynology alone cannot successfully identify species in this genus and should use comprehensive evidence to identify species.