Selaginells does not produce seed but spermopsida produce when both are heteroporous, why?

This is because Selaginella reproduces by two methods namely; vegetative and by formation of spores. In vegetative it takes place through fragmentation, tubers and resting buds while in formation of spores it takes through spore producing organs, strobilus, microsporangium and megasporangium. In all these processes, there is no production of seeds unlike in spermopsida.