All plants have a life cycle that alternates between diploid sporophyte and haploid gametophyte generations, and between sexual and asexual reproduction. In nonvascular plants, the gametophyte generation is dominant. vascular plants, the sporophyte generation is dominant, seedless vascular plants, such as reproduce with spores. Seed plants reproduce with pollen and eggs cones or flowers. Pollination must occur for fertilization to take place and seeds to develop.