CHLOROPLAST DNA POLYMORPHISM AT THE INTRA GENERIC LEVEL AND PLANT PHYLOGENIES

Analysis of chloroplast DNA (cpDNA) sequences is a tool which is being used more and more frequently in plant systematics and evolution. The recent development of polymerase chain reaction (PCR) has enabled seq uencing the rbcL gene for a great number of species and to infer phylo gemies at higher taxonomic levels. However this gene reaches its lower limits of resolution in resolving relationships among closely related genera. The analysis of non-coding regions, which display higher muta tion rates than coding regions, extends the resolution of the molecule . Here we report a high variability in divergence rates for two non-co ding regions of the chloroplast genome. Thirty-six species belonging t o 10 different genera were sampled and indicated divergence rates that varied 5-8 fold. In order to explain this heterogeneity, three non-ex clusive hypotheses involving sampling bias, age of common ancestor and variants of the molecular clock, are proposed and discussed. The pote ntial utility of these two non-coding regions in resolving phylogeneti c relationships differs among genera.