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

Abstract

ABSTRACT Pollen morphology of 12 species, representing tribes Brassiceae, Conringieae, Isatideae, and Plagiolobeae genera 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. The results revealed that pollen grains in these genera were tricolpate and their shapes varied from prolate to perprolate, with the polar axis ranging from 30.28 to 41.05 µm and the equatorial axis from 17.21 to 23.36 µm. However fine details are characteristic of distinguishing pollen grains in the species of the genera. The exine ornamentation varied among genera within the tribes and species within the same genus. Three pollen types are distinguished based on lumen size. All the studied tribes’ pollen were heterogeneous with ornamentation reticulate, ornamentation microreticulate (Conringia orientalis, Plagioloba derakii), and ornamentation macroreticulate (Moricandia sinaica). The exine thickness ranged from 0.75 to 2.60 µm. 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 tribes Isatideae and Brassiceae; (iii) confirmation of the transfer of P. crenulata from Zuvanda to Plagioloba, and I. planisiliqua from Conringia to Iljinskaea, respectively. Plagioloba clavata have great variations in the pollen morphological characters in Plagioloba and needs to be further studied. The key to the species of the genera was also provided.