. "14 Toward a New Synthesis: Major Evolutionary Trends in the Angiosperm Fossil Record." Variation and Evolution in Plants and Microorganisms: Toward a New Synthesis 50 Years after Stebbins. Washington, DC: The National Academies Press, 2000.
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Variation and Evolution in Plants and Microorganisms: TOWARD A NEW SYNTHESIS 50 YEARS AFTER STEBBINS
Stebbins wrote in “Fossils, Modern Distribution Patterns and Rates of Evolution,” chapter 14 of Variation and Evolution of Plants (Stebbins, 1950), about the disjunct distribution of modern genera of fossil plants. His rates of evolution were based on the various modern genera described in the fossil record of North America and currently living in southeastern Asia or South America. His arguments about the rates of evolution from the fossil record may have some validity when based on fossils from the Miocene (about 25 million years) and younger. However, many of the fossils from the Paleocene, Eocene, and Oligocene reported as living genera have been subject to revisions (Manchester, 1994) as shown in Fig. 2. This trend that had dominated angiosperm paleobotany for more than 100 years continued into the early 1970s. The supposed failure of the fossil record to contribute to understanding the evolution of the early angiosperms was still evident in 1974 when Stebbins published Flowering Plants:Evolution Above the Species Level (Stebbins, 1974). In chapter 10, “The Nature and Origin of Primitive Angiosperms,” there is no substantive use of the fossil record to address this question. The theories and hypothesis
FIGURE 2. Representation of the Middle Eocene Clarno Flora from eastern Oregon (Manchester, 1994) based on several thousands of fruits and seeds collected over 60 years. The bars represent the percent of the genera identified to angiosperm genera of various degrees of similarity to living genera. Note that less than 30% of the fruits and seeds can be identified with living genera.