Dr. Jeffrey Palmer and colleagues at the University of Michigan are studying evolutionary relationships among flowering plants at two distinct taxonomic levels. At one level, they plan to investigate relationships among the 50 or so families that comprise the subclass Asteridae, the second largest subclass of dicots. Although Asteridae are generally considered to be the most highly advanced and recently evolved of dicots subclasses, outstanding questions and controversies remain concerning the relative placement and relationships of most of the families in this group. In addition, there are fundamental doubts about whether the group as a whole is a natural, monophyletic one or an assemblage of parallel derivatives. Palmer will address this controversy by constructing a detailed phylogeny for the subclass using recently developed techniques of molecular systematic analysis. He will examine the distribution within this group and determine the phylogenetic significance of a number of defined chloroplast DNA rearrangements. He will also examine sequence variation in the chloroplast gene encoding the large protein subunit of the key photosynthetic enzyme, ribulose bisphosphate carboxylase. The second set of studies involves construction of a detailed molecular phylogeny for genera and tribes of the family Solanaceae of subclass Asteridae. This will greatly aid our understanding of evolutionary trends and relationships in this, the economically most important family in the subclass and also one of its largest. Despite the wide range of studies conducted on the biology and systematics of this important group of plants, which includes such vital crops as potatoes, tomatoes, and chili peppers, fundamental disagreements still exist regarding taxonomic relationships in the family. Palmer's approach here will involve comparative mapping of chloroplast DNA restriction site mutations and computer-assisted construction of phylogenetic trees based on these chloroplast DNA mutations.
