Distribution and Ecological Significance of Seed-Embryo Types in Mediterranean Climates in California, Chile, and Australia

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The ability of a seed to germinate and grow quickly under favorable conditions provides a competitive advantage. In semiarid climates, rapid germination improves the chances that a seedling will be able to utilize the brief period when moisture is available. The ability of an embryo within a seed to develop rapidly is partly related to the type of food storage in that seed. Seeds differ in internal morphology, ranging from those with small embryos and storage materials in adjacent tissues such as endosperm, to those with large embryos and storage materials within the cotyledons of the embryo. The possession of embryos and copious endosperm has been interpreted as a primitive condition in seeds (Stebbins 1974). In his discussion of the evolutionary trend from food storage in endosperm to food storage in the cotyledons, Stebbins states: “Most families and genera having [food storage in the cotyledons] consist of woody plants that possess vigorous seedlings, suggesting that the substitution of food material in the cotyledons for that in the endosperm somehow increases the speed and efficiency of germination and the vigor of the seedlings.” These observations have stimulated questions about the effects of embryo size and development on germination ecology and plant distribution, and suggest that placement of food storage is a character that has been acted upon by selective forces.