DOCUMENTATION OF RETICULATE EVOLUTION IN PEONIES (PEONIA) USING INTERNAL TRANSCRIBED SPACER SEQUENCES OF NUCLEAR RIBOSOMAL DNA - IMPLICATIONS FOR BIOGEOGRAPHY AND CONCERTED EVOLUTION

The internal transcribed spacers (ITS) of nuclear ribosomal DNA of 33 species of genus Paeonia (Paeoniaceae) were sequenced. In section Paeo nia, different patterns of nucleotide additivity were detected in 14 d iploid and tetraploid species at sites that are variable in the other 12 species of the section, suggesting that reticulate evolution has oc curred, Phylogenetic relationships of species that do not show additiv ity, and thus ostensibly were not derived through hybridization, were reconstructed by parsimony analysis. The taxa presumably derived throu gh reticulate evolution were then added to the phylogenetic tree accor ding to additivity from putative parents. The study provides an exampl e of successfully using ITS sequences to reconstruct reticulate evolut ion in plants and further demonstrates that the sequence data could be highly informative and accurate for detecting hybridization. Maintena nce of parental sequences in the species of hybrid origin is likely du e to slowing of concerted evolution caused by the long generation time of peonies, The partial and uneven homogenization of parental sequenc es displayed in nine species of putative hybrid origin may have result ed from gradients of gene conversion. The documented hybridizations ma y have occurred since the Pleistocene glaciations. The species of hybr id origin and their putative parents are now distantly allopatric. Rec onstruction of reticulate evolution with sequence data, therefore, pro vides gene records for distributional histories of some of the parenta l species.