Phylogeny and biogeography of woody plants
A phylogeny is the evolutionary history of a species or group of species—its genealogy. Phylogenetic studies help us understand how species are related, the changes that have led to the development of different groups, and the approximate time those changes took. Tracing the phylogeny of a plant group requires the use of evidence from various disciplines of biology, such as morphology, cytology, chemistry, and molecular biology (the term applied to the use of molecules—protein and DNA—in studying evolutionary relationships). Biogeography is the study of how plant groups got to where they are today; it seeks to learn what may have engendered the origin, dispersal, and extinction of plant groups in different geographic areas.
This project concentrates on the phylogeny and biogeography of many groups of woody plants. The first is the Coniferales, which include pines, spruces, larches, and yews. The goal is to determine whether the Coniferales form a natural group —that is, a closely related biological group—by using both morphological and DNA data to reconstruct the evolutionary history of its members. Currently, researchers are gathering plant material from all around the world to produce a collection that represents all conifer families and genera and 80 percent of the 500 species. This is an ambitious goal with potential long-term benefits for academic communities, the green industry, and the general public. We will establish a framework of evolutionary relationships for major groups within the Coniferales and provide a foundation for further studies at species and population levels. A clear understanding of genetic relationships of species can also guide for cultivar selection and breeding.
The second plant group includes 91 disjunct genera, each with species that occur naturally in both eastern Asia and North America. The goal here is to understand why so many plant genera display a very similar distribution pattern and to learn whether these geographic distributions follow a general pattern of formation. For example, one of the questions is whether North American species of a genus are more closely related to one another than any of them is to eastern Asian species of the genus. Recent studies have shown that there are complex evolutionary patterns in disjunct genera. It is important to investigate the patterns and their correlation with geological times and events. By integrating knowledge from evolutionary history, ecology, and geology, this project will provide a basis for understanding changes in biodiversity over time and for predicting how vegetation will react to ever-increasing human impacts.
The third group being studied consists of economically and horticulturally important plants, especially those that are problematic taxonomically (e.g., Betula, birches; and Acer, maples). Phylogenetic studies will help define natural groups and trace the evolutionary pathways of important features, such as fall foliage in maples and gene duplication and chromosome doubling in some species of birches and maples. Often, plant breeders select cultivars so different from their parents that it is impossible to tell the parentage of cultivars. Nevertheless, DNA can provide unequivocal answers since vegetative selections generally do not change plant DNA constituents and hybrids carry genetic contents from both parents. In addition, Recent work in developmental genetics has identified the genes responsible for regulating certain morphological and physiological traits. By comparing the DNA information in the genes of some of horticultural plants with that of their parents, we can study the correlation between changes in genes and those in the morphology.