Evolution in Early Seed Plants: Calamopityaceae and Early Medullosales in North America

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Seed-bearing plants (flowering plants, conifers, and their relatives) are by far the dominant elements of modern terrestrial habitats. However, the fossil record clearly reveals that this was not always the case. The first evidence of seed plants comes from Upper Devonian sediments of North America (360 million years ago), where they represent only one of several very successful major plant groups. At present there is considerable debate over the evolutionary relationships of these early land plants, and the processes at work leading to the eventual dominance of seed plants. Drs. Charles Beck and William Stein of the University of Michigan have assembled the most extensive collection of these early Devonian and Carboniferous age seed plants. Their research includes: careful documentation of developmental changes in morphology in shoot systems; analysis of the architecture of primary vascular tissues; computer-aided description of cell and tissue patterns in sections of fossil material; and assessment of the evolutionary significance of variation among early seed plants and their presumed spore-bearing relatives. Their work will help determine the phylogenetic relationships and early origins of the seed plants.