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

有种子的植物（开花植物、针叶树和它们的亲戚）是现代陆地栖息地的主要组成部分。然而，化石记录清楚地表明，情况并非总是如此。种子植物的第一个证据来自北美（3.6亿年前）的上泥盆世沉积物，它们只是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主导地位的过程，存在着相当大的争论。Drs。密歇根大学的查尔斯·贝克和威廉·斯坦收集了最广泛的这些早泥盆纪和石炭纪的种子植物。他们的研究包括：仔细记录芽系统形态的发育变化；初生维管组织的结构分析；化石材料切片中细胞和组织模式的计算机辅助描述；评估早期种子植物及其假定的有孢子亲缘植物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.