Chloroplast DNA variation and reticulate evolution in sexual and apomicticsections of dandelions

Sequencing of the trnL-trnF intergenic spacer in chloroplast DNA (cpDNA) fr om 237 sexual and apomictic species of dandelions (genus Taraxacum) from Eu rope, Asia and arctic North America revealed 46 haplotypes, which differed mainly by a variable number of polymorphic tRNA pseudogenes next to the trn F gene. The haplotypes could be divided into 20 cpDNA lineages, but indepen dent duplications and deletions of the pseudogene copies made it difficult to further reconstruct the phylogeny. Intraspecific cpDNA variation was fou nd in the primitive sexual T. serotinum. However, in contrast to a recent s tudy, no cpDNA variation was detected within 12 apomictic species represent ing a variety of haplotypes. The cpDNA haplotype may therefore help to defi ne these critical apomicts. On the other hand, the genetic variation may ea sily be overestimated, if the clones are not correctly identified, because some morphologically similar microspecies carried very different haplotypes . In all, 36 sections of the genus were sampled. Four primitive, mainly sex ual, sections only displayed a group of ancient haplotypes, whereas morphol ogically more advanced sections often exhibited many different haplotypes f rom up to seven cpDNA lineages. In the latter cases, the lineages were rare ly unique to a certain section. For ex ample, the two most widespread haplo types, belonging to different lineages, were found together in nine section s. This suggests that significant gene flow has occurred among the advanced sections, although sexual reproduction is not currently known in several o f them. The result is consistent with the reticulate distribution of morpho logical characters among the sections.