The evolution of seeds

SummaryThe evolution of the seed represents a remarkable life‑history transition for photosynthetic organisms. Here, we review the recent literature and historical understanding of how and why seeds evolved. Answering the 'how' question involves a detailed understanding of the developmental morphology and anatomy of seeds, as well as the genetic programs that determine seed size. We complement this with a special emphasis on the evolution of dormancy, the characteristic of seeds that allows for long 'distance' time travel. Answering the 'why' question involves proposed hypotheses of how natural selection has operated to favor the seed life‑history phenomenon. The recent flurry of research describing the comparative biology of seeds is discussed. The review will be divided into sections dealing with: (1) the development and anatomy of seeds; (2) the endosperm; (3) dormancy; (4) early seed‑like structures and the transition to seeds; and (5) the evolution of seed size (mass). In many cases, a special distinction is made between angiosperm and gymnosperm seeds. Finally, we make some recommendations for future research in seed biology. Contents Summary 817 I. Introduction 818 II. Seed development 819 III. Evolution and functions of the endosperm tissue 821 IV. Evolution of dormancy 822 V. Early seed‑like structures and the transition to seeds 824 VI. Seed size evolution 825 VII. Conclusion 828 Acknowledgements 828 References 828