Tansley Review - New Phytologist 186: 817-831 (2010)

The evolution of seeds

Abstract
The 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. Here we will compliment this with a special emphasis on the evolution of dormancy, the characteristics of seeds which allows for long ‘distance’ time travel. Answering the ‘why’ question involves proposed hypotheses of how natural selection has operated to favour the seed life history phenomenon. Here we will review the recent flourish of research describing the comparative biology of seeds. 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 will be made between angiosperm and gymnosperm seeds. In the end we make some recommendations for future research in seed biology.

Contents:
Summary
I. Introduction
II. Seed development
III. Evolution and functions of the endosperm
IV. Evolution of dormancy
V. Early seed-like structures and the transition to seeds
VI. Seed size evolution
VII. Conclusions

Key words: seed evolution • seed dormancy • seed mass • endosperm • perisperm • gymnosperms • angiosperms • comparative seed biology • seed development

Think of the fierce energy concentrated in an acorn!
You bury it in the ground, and it explodes into an oak!
Bury a sheep, and nothing happens but decay.
George Bernard Shaw

Financial support: Our work is supported by the Deutsche Forschungsgemeinschaft (DFG grants LE 720/6 and LE 720/7) and the ERA-NET Plant Genomics grant vSEED to GLM, and by a sabbatical grant to CK by California Polytechnic State University.