A process in many plants resulting in the fusion of a female gamete and a male gamete to form a single cell, the zygote. Both vegetative (asexual) reproduction and sexual reproduction occur in plants. Reproduction by gamete fusion is very different from vegetative reproduction, which is a common mode of multiplication in many plants. Several steps can be distinguished in the fertilization process. First, the haploid male and female gametes have to be brought into proximity. The cell membranes of the two gametes then fuse (plasmogamy), resulting in a single cell, the zygote. The nuclear membranes next fuse (karyogamy), producing a cell with a single diploid nucleus. There is a wide variety of ways by which the male and female sex cells of the different groups of plants are produced and make contact with each other prior to fertilization. Among the more primitive plants, fertilization occurs between free-swimming male and female gametes. In somewhat more advanced plants, the female gamete is stationary and partly enclosed by other cells, but the male gametes are motile. In the most highly evolved plants, the flowering plants, fertilization takes place between nonmotile gametes in the female reproductive organ.