The dicotyledonous angiosperm family Cactaceae (the Cactus Family) will be examined for systematically-useful variation in the chloroplast genome. DNA samples of representative taxa from throughout the family will be analyzed for gene sequence variation in the chloroplast-encoded gene for ribulose bisphosphate carboxylase large subunit (rbcL). Studies of gene sequence variation will be used to address long-standing questions about the phylogenetic relationships within the family at the subfamilial and tribal levels, as well as to assess monophyly of previously proposed taxonomic groups. Data derived from rbcL gene sequencing will be integrated with morphological data obtained from comparative studies of structural characters such as those of spines, flowers, fruits, and seeds, and will be analyzed to develop hypotheses about the relationships within and between subfamilies of the Cactaceae, and within the tribes of the subfamilies Cactoideae and Opuntioideae. Cladistic analysis of DNA data together with morphological data will provide additional information from which inferences may be made to assist in understanding the complex phylogeny, morphological diversification, and biogeographic radiation of the cacti.
