The ultrastructure and reproductive significance of Lasiostrobus microspores

The normally inaperturate microspores of the Pennsylvanian cone Lasiostrobus are found to rarely possess trilete sutures, confirming the subequatorial position of the sacci. Sporoderm ultrastructure compares favourably with saccate pollen of some extant members of the Coniferales. The shedding of grains in the microspore stage suggests that microgametophyte evolution had passed the stage of prothallial cell production, and that Lasiostrobus is an advanced member of the Paleozoic gymnosperm complex.