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

到目前为止，种子植物(开花植物、针叶树及其近亲)是现代陆地栖息地的主要成分。然而，化石记录清楚地表明，情况并不总是如此。种子植物的第一个证据来自北美上泥盆纪的沉积物(3.6亿年前)，在那里它们只代表了几个非常成功的主要植物群中的一个。目前，关于这些早期陆地植物的进化关系，以及导致种子植物最终占优势的过程，存在着相当大的争论。密歇根大学的查尔斯·贝克博士和威廉·斯坦博士收集了最广泛的这些早期泥盆纪和石炭纪时代的种子植物。他们的研究包括：仔细记录枝条系统形态的发育变化；分析初级维管组织的结构；计算机辅助描述化石材料切片中的细胞和组织模式；以及评估早期种子植物及其可能具有孢子的近亲之间变异的进化意义。他们的工作将有助于确定种子植物的系统发育关系和早期起源。

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.