While the possession of vascular tissue and the production of seeds, also characteristic of the gymnosperms, have undoubtedly played a part in the success of the flowering plants, it is the flower that may well be the single most important factor responsible for the abundance of species. Many flowering plants have benefited from evolutionary associations with their animal pollinators. This association, better known as coevolution , most likely has driven much of this recent and rapid diversification. Given their agricultural, horticultural, and overall economic importance, it is not surprising that the angiosperms have been the major focus of plant propagators, who have developed numerous propagation techniques.
Flowers are where sexual reproduction occurs in angiosperms.
Pollination is the transfer of pollen grains from an anther, the structure where these grains are produced, to a stigma, a structure or surface receptive to pollen. If conditions are right, each pollen grain will produce a tube that grows down through the style and into an egg-containing ovule in the ovary, where it deposits two sperm. Fertilization occurs when a sperm unites with the egg. In angiosperms, a second remarkable event occurs when the second sperm unites with additional material in the ovary. The ovule, with its now-fertilized egg, develops into a seed, while at the same time the ovary develops into a fruit.