Practice question

Seed plants universally produce heterospores, yet only angiosperms perform double fertilization as defining synapomorphy separating them from gymnosperms. Pollen tube delivers two non-motile sperm; one fuses with haploid egg generating diploid zygote, second fuses with homodiploid central cell bearing two polar nuclei creating triploid primary endosperm nucleus. Endosperm develops rapidly post-fertilization provisioning embryo, avoiding resource investment without fertilization economizing maternal resources. Gymnosperms display single fertilization with haploid female gametophyte storage provisioned beforehand. Naked seeds, vessel elements and floral envelope vary across clades, hence fertilization biology remains most reliable discriminator for classification used in advanced plant systematics.