Microsatellite variation, sexual reproduction and taxonomic revision of Taraxacum sect. Dioszegia: relationships at a large spatial scale.

The coexistence of agamospermy and sexuality characterizes most of the ~60 sections of the genus Taraxacum. Section Dioszegia, comprising T. serotinum and its allies, are an exception because only sexuals are reported for all the members of this group. On the basis of the analysis of microsatellite (SSRs) variation, distribution and morphology, we addressed problems related to their mode of reproduction, among-population relationships, taxonomy and within-population variation, using samples from populations in an area extending from southern France to the European part of southern Russia and Iran. We found strong isolation by distance and deep spatio-temporal structure among populations. As a rule, outcrossing was the dominant mode of reproduction, with one notable exception: T. serotinum subsp. tomentosum (≡ T. pyrrhopappum) was autogamous and not heterozygous. This subspecies is understood as a relic of a continental migration of T. serotinum in the late glacial/early post-glacial period, which became autogamous. Taraxacum haussknechtii is relatively highly heterozygous with a high degree of connectivity among populations, whereas populations of T. serotinum subsp. serotinum show high level of inter-population variability. A taxonomic revision of sect. Dioszegia recognizes T. serotinum subsp. serotinum (including an aberrant taxon, newly described as var. iranicum), T. serotinum subsp. tomentosum and T. haussknechtii. Full synonymy was compiled and lectotypes designated for six names. A list of the herbarium material studied is given for the latter three taxa, and a distribution map is provided for T. haussknechtii.