This question of why some branches of the tree of life explode into thousands of species, while others remain small, has shaped evolutionary biology since Charles Darwin.
My colleague and I have published a new study of cactus flowers which may help explain the conundrum.
For more than a century, scientists have seen flowers that are specialised to a particular pollinator or environment as drivers of the evolution of new diversity. Our new research challenges that idea, which could change how scientists think about the forces that create biodiversity across the plant world.
