CHLOROPLAST DNA PHYLOGENY, RETICULATE EVOLUTION, AND BIOGEOGRAPHY OF PAEONIA (PAEONIACEAE)

The coding region of the matK gene and two intergenic spacers, psbA-tr nH and trnL(UAA)-trnF(GAA), of cpDNA were sequenced to study phylogene tic relationships of 32 Paeonia species. In the psbA-trnH intergenic s pacer, short sequences bordered by long inverted repeats have undergon e inversions that are often homoplasious mutations. Insertions/deletio ns found in the two intergenic spacers, mostly resulting from slipped- strand mispairing, provided relatively reliable phylogenetic informati on. The matK coding region, evolving more rapidly than the tmL-trnF sp acer and more slowly than the psbA-trnH spacer, produced the best reso lved phylogenetic tree. The matK phylogeny was compared with the phylo geny obtained from sequences of internal transcribed spacers (ITS) of nuclear ribosomal DNA. A refined hypothesis of species phylogeny of se ction Paeonia was proposed by considering the discordance between the nuclear and cpDNA phylogenies to be results of hybrid speciation follo wed by inheritance of cpDNA of one parent and fixation of ITS sequence s of another parent. The Eurasian and western North American disjunct distribution of the genus may have resulted from interrruption of the continuous distribution of ancestral populations of extant peony speci es across the Bering land bridge during the Miocene. Pleistocene glaci ation may have played an important role in triggering extensive reticu late evolution within section Paeonia and shifting distributional rang es of both parental and hybrid species.