PHYLOGENETIC-RELATIONSHIPS AND PATTERNS OF CHARACTER CHANGE IN THE TRIBE LACTUCEAE (ASTERACEAE) BASED ON CHLOROPLAST DNA RESTRICTION SITE VARIATION

The Lactuceae is perhaps the most easily recognizable tribe in the Ast eraceae, distinguished by the presence of milky latex and of ligulate florets in the inflorescence. Three existing taxonomic treatments of t he tribe establish subtribal classifications but fail to resolve relat ionships among major lineages. Our study of chloroplast DNA restrictio n site variation sampled 60 Lactuceae taxa. We detected 1268 mutations , 612 of which are phylogenetically informative. Despite the large amo unt of variation detected, little resolution of relationships among ma jor lineages was obtained from parsimony analyses, although the monoph yly of many groups is strongly supported. These results, when consider ed along with data from morphological analyses of other workers, sugge st that rapid diversification played an important role in early stages of the tribe's evolution. Our examination of character change further reveals that as noted by other workers, restriction site variation is not evenly distributed across the chloroplast genome and that regions with higher levels of variation do not necessarily have higher amount s of homoplasy. This is somewhat surprising, since we found that amoun ts of homoplasy along terminal branches of our phylogenetic tree are r elated to levels of divergence.