Although they are relative latecomers on the evolutionary scene, having emerged only 135-170 million years ago, angiosperms--or flowering plants--are the most diverse and species-rich group of seed-producing land plants, comprising more than 15,000 genera and over 350,000 species. Not only are they a model group for studying the patterns and processes of evolutionary diversification, they also play major roles in our economy, diet, and courtship rituals, producing our fruits, legumes, and grains, not to mention the flowers in our Valentine's bouquets. They are also crucial ecologically, dominating most terrestrial and some aquatic landscapes. -- Back cover.