Phylogenetic relationships among higher taxa of plants (subclasses, orders, families) often are widely disputed, particularly within a number of troublesome tropical-temperate sister-family pairs. A classic example of the tropical-temperate sister-family problem is exemplified by two families usually placed within Apiales: the tropical, woody Araliaceae and the temperate, herbaceous Apiaceae. Further disputed is the relationship of Apiales to other order (Cornales, Pittosporales, Asterales), as well as the relationships within each family, especially Apiaceae, in which there are three subfamilies (Apioideae, Saniculoideae, and Hydrocotyloideae). Phylogenetic relationships at the ordinal and interfamilial levels will be examined using comparative gene sequencing of the chloroplast gene rbcL. Comparative sequencing of the much more rapidly-changing ORFK will be used to elucidate infrafamilial relationships. Preliminary studies to date indicate that a contracted Inverted Repeat characterizes some, but not all, species of Apioideae. The taxonomic distribution of this chloroplast genome rearrangement will therefore be examined in detail to help resolve relationships in Apiaceae. The character state changes of certain morphological traits will also be examined in light of the molecular phylogeny. Preliminary data indicate that many of the traditional concepts of relationships in Apiales are inaccurate and that further sampling of representative taxa will greatly increase our understanding of this order. This study will, therefore, provide an important model for the examination of other tropical-temperate sister families.
