Along with the origins of vascular plants and seed plants, the origin of flowering plants represents one of the three most significant evolutionary radiations of land plants during the last 475 million years. With over 250,000 extant species, angiosperms are the largest and most diverse group of plants ever to have evolved. Paradoxically, we know less about the origin and early evolutionary history of angiosperms than we do about many considerably older groups of land plants. Indeed, Darwin’s “abominable mystery” continues to challenge evolutionary biologists. Our research efforts have focused on the evolution of double fertilization and endosperm, two of the most important and defining features of flowering plants. These analyses of the origin of the angiosperm reproductive syndrome have drawn upon a variety of approaches from developmental biology to inclusive fitness theory.