The answer to your question is flowering plants are the most recently evolved of the major groups of plants, arising only about 130 million years ago. Despite their geological youthfulness, angiosperms are the dominant plants of the world today: about 80% of all living plant species are flowering plants. Furthermore, they occupy a greater variety of habitats than any other group of plants. The ancestors of flowering plants are the gymnosperms , which are the other major group of plants that produce seeds. The gymnosperms, however, produce their seeds on the surface of leaf-like structures, which makes the seeds vulnerable to mechanical damage when winds whip the branches back and forth, and to drying out. Most importantly, conifer seeds are vulnerable to insects and other animals, which view seeds as nutritious, energy packed treats. In angiosperms, the margins of the seed-bearing leaves have become inrolled and fused, so the seeds are no longer exposed but are more safely tucked inside the newly evolved "vessel," which is the ovary.
The other major advance of the angiosperms over the gymnosperms was the evolution of the flower, which is the structure responsible for sexual reproduction in these plants. The function of sexual reproduction is to bring together genetic material from two individuals of differing ancestry, so that the offspring will have a new genetic makeup.
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