A POPULATION GENETIC-ANALYSIS OF CHLOROPLAST DNA IN PHACELIA

Hierarchical sampling from populations, incipient and recognized varie ties within Phacelia dubia and P. maculata has revealed high levels of intraspecific polymorphism in chloroplast DNA. Much of the variation is partitioned between populations as evidenced by population-specific variants at fixation in all three populations of P. dubia var. interi or and in both populations of P. maculata. Nine of 16 populations were polymorphic for cpDNA haplotypes. A total of 16 haplotypes was found in a sample of 106 individuals; the most common occurred in eight of t he 16 populations and in 31 per cent of the individuals in the entire sample. A phylogenetic analysis revealed four basic plastome types. Th e two major groups of plastomes were separated by four independent bas e-pair mutations which suggests an ancient split in the evolution of p lastid genomes. Representatives from each major plastome division were found in each of five populations spanning two allopatric varieties o f P. dubia. The geographical distribution of haplotypes and lack of ev idence for recent admixture argue against migration as a source of the polymorphism. It is more likely that the current taxonomic varieties are descendants of a polymorphic common ancestor.