Pollen morphology of some selected species of the tribes Brassiceae, Conringieae, Isatideae, and Plagiolobeae (Brassicaceae) in Iran, and its taxonomic significance

Pollen morphology of 12 species, representing genera of the tribes Brassiceae, Conringieae, Isatideae and Plagiolobeae were studied using light microscopy (LM) and scanning electron microscopy (SEM). The results demonstrated that the polar diameter, pollen exine ornamentation, mesocolpium width, and exine thickness have important systematic significance. Pollen grains in these genera were tricolpate and their shapes varied from prolate to perprolate, with the polar axis length ranging from 30.28 to 41.05 mu m and the equatorial axis length ranging from 17.21 to 23.36 mu m. However, fine details can be used to distinguish pollen grains of the different species within the genera. The exine ornamentation varied among genera within the tribes and among species within the same genus. Three pollen types are distinguished based on lumen size. All the studied tribes' pollen were heterogeneous, with reticulate, microreticulate (Conringia orientalis, Plagioloba derakii), or macroreticulate (Moricandia sinaica) ornamentation. The exine thickness ranged from 0.75 to 2.60 mu m. Pollen characteristics support: (i) two distinct pollen types (viz. Conringia austriaca and Iljinskaea planisiliqua types) in all four tribes; (ii) the similarity of the pollen shape between tribes Isatideae and Brassiceae; (iii) the transfer of P. crenulata from Zuvanda to Plagioloba, and of I. planisiliqua from Conringia to Iljinskaea. Plagioloba clavata displays great variation in pollen morphological characters and needs to be further studied. A key to the species of the genera was also provided.