Embryogenesis has evolved independently in plants and animals. Comparative studies in animals have pointed towards an hourglass pattern of embryo development where early events are less conserved across species but lead to a highly conserved middle period, before diversifying again.
Cridge et al. explore comparative morphological studies and more recent molecular work in plants to ask if a similar hourglass pattern of embryogenesis exists. They then discuss what convergent evolution of such a pattern in plants and animals tells us about the developmental constraints imposed upon embryogenesis and the evolution of the underlying gene regulatory networks.