ABSTRACT
This chapter reviews the phylogenetic impact and promise of a relatively new set of molecular tools—DNA sequence and restriction endonuclease analysis—as applied to a specific DNA molecule, the chloroplast genome of flowering plants. Relationships for Brassica species at the level of the nuclear genome, based on cytogenetic and crossing studies, are expressed by the triangle of U. Early molecular studies on the genus Nicotiana were quite limited in scope, but did at least point to the potential of chloroplast DNA comparisons for illuminating relationships. In spite of the large number of studies that have exploited chloroplast DNA restriction fragment variation for phylogenetic purposes, there has been relatively little effort in developing methods for constructing phylogenetic trees from this variation. Finally, that chloroplast DNA is maternally inherited in Brassica, as in most plants, allows insight into the direction of interspecific crosses that is virtually unparalled.
