Molecular Systematics of the Malpighiaceae

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The Malpighiaceae are a medium-sized family of tropical and subtropical flowering plants, comprising about 65 genera and 1200 species, with 85% of the species native to the New World, the rest found in the Paleotropics. The family is internally homogeneous and externally isolated, that is, the members all look a great deal alike and are clearly related, but do not closely resemble any other family. Traditional systematic methods, relying principally on gross morphology, have failed to resolve many questions of relationships within the family, because of the aforementioned similarity, and also to reveal where this family fits into the larger group of relatively unspecialized flowering plants (related to the rose group) whose flowers have free parts in whorls of five. The research proposed by Dr. Mark Chase at University of North Carolina and Dr. William Anderson at University of Michigan is designed to apply new, molecular techniques to these old, intractable problems. The chloroplasts of green plants contain numerous circular chromosomes, which are relatively easy to characterize because they hold so much less DNA than the huge nuclear genome. Several researchers have had great success in recent years at using comparative studies of chloroplast DNA (cpDNA) to resolve problems in plant systematics. Drs. Chase and Anderson plan to study the cpDNA of the Malpighiaceae and representatives of several putatively related families in two quite different ways, attempting to answer questions about relationships within the family and between families. Nucleotide sequencing of selected cpDNA genes will allow construction of an informative phylogenetic hypothesis for Malpighiaceae and related families. Then, using the technique of restriction site mapping, they plan to compare the cpDNA of 60 species of Malpighiaceae that represent most of the diversity within the family. The within- family phylogeny will resolve questions about whether functionally analogous and even morphologically similar fruits have evolved once or several times in parallel; how the genera are related to one another; and which of two diametrically opposed hypotheses about the place of origin of the family and the nature of the earliest members is correct. Collaboration between the two workers, which combines the strengths of traditional morphological systematics with a modern molecular approach, should serve as a model for future collaboration between other traditional and molecular systematists.