Phylogeny and Evolution of Caesalpinioid Legumes

点击翻译按钮获取中文摘要

The Leguminosae (or Fabaceae - the legume or bean family) is the third largest family of flowering plants, and the second most important family economically. Legumes range from giant rain forest trees to tiny herbaceous annuals of desert habitats. Of the three traditionally recognized subfamilies, Caesalpinioideae, Mimosoideae, and Papilionoideae, the Caesalpinioideae is the most poorly known because it is largely confined to tropical habitats. As a consequence, evolutionary relationships among caesalpinioid legumes are poorly known and the recognition of particular genera is often in dispute. Previous work by Dr. Herendeen and his colleagues in Canada and England has developed a general phylogenetic framework for Caesalpinioideae, which will be used to further research on morphology, taxonomy, and phylogeny. Current morphological and molecular data show that several caesalpinioid lineages have more basal positions than either the Mimosoideae or Papilionoideae. Thus a classification system for the family based on evolutionary relationships would not recognize the caesalpinioids as a single natural unit but as several early-branching lineages. How many distinct lineages of caesalpinioid legumes are there, at what level should they be recognized relative to mimosoids and papilionoids, what are the relationships among caesalpinioid genera, and what can we discern about patterns of morphological evolution? These questions form the core of the study. The primary goal of this research is to produce a classification that includes all ca. 160 genera of caesalpinioid legumes based on analyses of data from morphology and DNA sequence data. To achieve this, field work will be conducted in Madagascar, South America, and SE Asia to obtain material of as many of the missing genera as possible. The investigators will also study collections in herbaria and prepare anatomical samples to score morphological characters for all species included in the molecular data set. They will use the phylogenetic results to produce a revised classification and identification key to subfamilies, tribes, and genera for all caesalpinioid legumes. With a robust phylogeny and a specimen-based morphological data set, they will be able to explore the implications of the phylogeny with respect to patterns of morphological evolution. In addition, data on a diverse array of fossil legumes will be integrated with the results. The fossils may be used in documenting minimum ages of clades and as historical data points for biogeographic studies. In addition, molecular clock techniques will be used to estimate ages of clades. The data generated in this study will make the Leguminosae an ideal group in which to experiment with new methods in estimating ages of clades and assessing rates of taxonomic diversification and molecular evolution.