Phylogenetics and Evolution of Crassula (Crassulaceae)

玉石植物（石竹属，石竹科）是一组大约200种开花植物，主要局限于南非。这些植物，虽然以其高度肉质的叶子而闻名，但它们的生长形式多种多样，从一年生植物到长寿的灌木和乔木。这一组的物种也显示出惊人的花朵多样性；一些物种有微小的星形花，而另一些有大的管状花。同样值得注意的是，一些玉石植物的染色体数目具有高度的多样性；然而，这种变化的意义还有待全面研究。在南非，玉石植物生长在许多不同的栖息地，其中许多生长在潮湿的悬崖表面，而另一些则局限于沿海沙丘栖息地。在该国的某些地区（如多肉的卡鲁沙漠），这些物种构成了植被的主要生态组成部分。尽管这些植物具有重要的生态意义和高度的形态多样性，但它们的分类尚未得到全面的研究。堪萨斯大学的马克·莫特博士和他在南非的同事们提出的这项研究主要集中在这一迷人而复杂的植物群上，并有几个主要目标：1)玉石植物物种之间的进化关系将通过比较来自多个基因区域的DNA序列来确定。这项研究将为研究生长形式、花和染色体数目的多样性提供一个必要的框架。综合起来，这将有助于评估这类植物的物种界限，并最终有助于确定应该识别多少物种。2)通过田间采集的花的17种形态特征的详细测量来评估花的多样性。这将为这个属的花的变化提供重要的见解。3)通过广泛的染色体计数来记录玉石植物的染色体多样性程度。染色体多样性的研究结合物种关系的估计，将使我们能够评估染色体变化在创造玉石植物中存在的物种多样性中的重要性。尽管南非面积相对较小，但其植物的多样性可与广为人知的热带地区相媲美。尽管它的独特性，这个地区的许多植物多样性还有待研究。考虑到当前和持续的对全球生物多样性的威胁，多样性集中的地区，如南非，需要特别关注。这项工作将有助于堪萨斯大学的研究生教育，目前正在与南非的植物学研究人员合作进行；研究结果将通过在美国和南非举行的非正式讲座向教育工作者和公众公布。

The jade plants (Crassula, Crassulaceae) are a group of approximately 200 species of flowering plants that are largely confined to South Africa. These plants, while best known for their highly fleshy leaves, display a great diversity of growth forms, ranging from annuals to long-lived shrubs and trees. Species in this group also display a spectacular diversity of flowers; some species possess tiny star-shaped flowers while others have large tubular flowers. Also noteworthy is the high diversity of chromosome numbers that have been reported for some species of jade plants; however, the significance of this variation has yet to be investigated comprehensively. In South Africa, jade plants occur in many different habitats, with many found on moist cliff faces, whereas others are confined to coastal sand dune habitats. In certain areas of the country (e.g. the Succulent Karoo Desert) these species form a major ecological component of the vegetation. Despite their ecological importance and high level of morphological diversity, the taxonomy of these plants has yet to be studied comprehensively. The proposed research by Dr. Mark Mort of the University of Kansas, with colleagues in South Africa, focuses on this attractive and complex group of plants and has several major goals: 1) Evolutionary relationships among species of jade plants will be determined through comparison of DNA sequences from multiple gene regions. This study will result in a necessary framework for examining the diversity in growth form, flowers, and chromosome numbers. In combination, this will permit an assessment of the boundaries of species within this group of plants and ultimately will assist in determining how many species should be recognized. 2) Floral diversity will be assessed via detailed measurements of approximately 17 morphological traits from field-collected flowers. This will provide important insights into floral change in this genus. 3) The extent of chromosome diversity in jade plants will be documented by conducting extensive chromosome counting. Examination of chromosome diversity in conjunction with the estimate of species relationships will permit an assessment of the importance of chromosome changes in creating the species diversity present in jade plants. South Africa, despite its relatively small size, contains a diversity of plants that is comparable to the more widely publicized tropics. Despite its uniqueness, much of the botanical diversity of this region has yet to be examined. Considering the current and ongoing threat to global biodiversity, areas of concentrated diversity, such as South Africa, require special attention. This work will contribute to graduate education at the University of Kansas and is being conducted in collaboration with botanical researchers in South Africa; the results will be communicated to educators and the general public through informal lectures in the U.S. and in South Africa.