Dissertation Research: Biosystematics and Evolution of the Genus Brachylaena R. Brown (Comlpositae)

Brachylaena(菊科)是13个种的木本雌雄异株属，它与菊科的其他成员不同，被认为是一个单系组合。Brachylaena中有5种是马达加斯加和马斯卡林群岛特有的，而8种仅限于非洲大陆。私人投资促进机构建议以短枝藻为样本，测试马达加斯加植物区系的一些拟议来源和亲缘关系。该属分布于这两个地区，在马达加斯加岛上分布广泛，暗示着一种古老的亲缘关系。一些分类学问题，如形态形态间的相互融合，已在该属中被认识，因此，建议进行初步的物候学分析，以确定该属的群的界限。然后对分析得到的群体进行比较，以确定个体物种种群内和种群之间的遗传变异，并估计该属物种之间的遗传差异。仅对该属进行了两次染色体计数，但从中似乎至少有一种是四倍体。除了表型和电泳学外，还将对叶绿体DNA的限制酶切点数据进行分析，以产生该属的系统发育假说。这将与形态生成的分支图进行比较。Brachylaena的分布，其中某些物种仅限于非洲大陆，其他物种仅为马达加斯加特有，这将使我们有可能在这两个地区的背景下讨论这一群体的演变，并将其与已知的地质事件联系起来。此外，该属的生物学和分布方面(即木本、雌雄异株和热带)使其成为研究种群内和种群间遗传变异的一个有趣和重要的群体。

Brachylaena (Compositae) is a woody, dioecious genus of thirteen species; it is distinct from other members of the Compositae and is considered to represent a monophyletic assemblage. Five of the species of Brachylaena are endemic to Madagascar and the Mascarene Islands while eight species are confined to the continent of Africa. The PIs propose to test some of the proposed origins and affinities of the Madagascar Flora using Brachylaena as an exemplar. The genus is distributed between the two regions and it is widespread on the Island of Madagascar, suggesting an ancient affinity. Several taxonomic problems such as intergrading morphological forms have been recognized in the genus therefore, it is proposed that an initial phenetic analysis be carried out to establish the limits of the groups. The groups obtained from this analysis will then be compared electrophoretically to determine the genetic variation within and among populations of individual species and to estimate the genetic divergence among species of the genus. Only two chromosome counts have been made for the genus but it appears from these that at least one of the species is tetraploid. In addition to phenetics and electrophoresis, an analysis of restriction site data from chloroplast DNA will be undertaken in order to produce a phylogenetic hypothesis for the genus. This will be compared to a cladogram generated from morphology. The distribution of Brachylaena, with certain species restricted to the continent of Africa and others endemic to Madagascar, will make it possible to discuss the evolution of this group in the context of the two regions and to relate this to known geological events. Furthermore, aspects of the biology and distribution of this genus (i.e., woody, dioecious and tropical) make it an interesting and important group in which to study genetic variation within and among populations.