Morphological studies of pollen grains of Medicago species in Iran

With more than 23 species of Medicago, Iran is one of the origins and centers of diversity of this genus. Due to close similarity in sexual organs and pod-characteristics, taxonomical classification of these species based on morphological characteristics is difficult. Scanning Electron Microscopy (SEM) was used to study the major characteristics of pollen grain among Iranian Medicago species. Pollen grains were mostly tricolpate, but quadricolpate or hexacolpate pollen grains were also observed in one species. The equatorial view was elliptic to rectangular or spherical shapes and the polar view was obtuse-triangular, truncate-triangular or square tips. Majority of species showed reticulate (perforate, faveolate, regulate and, scrobiculate) and verrucate exine surface. M. rigiduloides with quadric or hexic colpate pollen grain was barely distinguishable from M. rigidula with tricolpate pollen exine surface. On the other hand, M. tornata with its spherical pollen and verrucate exin surface was obviously different from M. polymorpha with rectangular pollen grain and reticulate exine surface. This is the first report of M. rigiduloides and M. tornata from Iran.