| Summary: | <p>Abstract</p> <p>Background</p> <p>Hybridisation is presumed to be an important mechanism in plant speciation and a creative evolutionary force often accompanied by polyploidisation and in some cases by apomixis. The <it>Potentilla collina</it> group constitutes a particularly suitable model system to study these phenomena as it is morphologically extensively variable, exclusively polyploid and expresses apomixis. In the present study, the alpine taxon <it>Potentilla alpicola</it> has been chosen in order to study its presumed hybrid origin, identify underlying evolutionary processes and infer the discreteness or taxonomic value of hybrid forms.</p> <p>Results</p> <p>Combined analysis of AFLP, cpDNA sequences and ploidy level variation revealed a hybrid origin of the <it>P. alpicola</it> populations from South Tyrol (Italy) resulting from crosses between <it>P. pusilla</it> and two cytotypes of <it>P. argentea</it>. Hybrids were locally sympatric with at least one of the parental forms. Three lineages of different evolutionary origin comprising two ploidy levels were identified within <it>P. alpicola.</it> The lineages differed in parentage and the complexity of the evolutionary process. A geographically wide-spread lineage thus contrasted with locally distributed lineages of different origins. Populations of <it>P. collina</it> studied in addition, have been regarded rather as recent derivatives of the hexaploid <it>P. argentea</it>. The observation of clones within both <it>P. alpicola</it> and <it>P. collina</it> suggested a possible apomictic mode of reproduction.</p> <p>Conclusions</p> <p>Different hybridisation scenarios taking place on geographically small scales resulted in viable progeny presumably stabilised by apomixis. The case study of <it>P. alpicola</it> supports that these processes played a significant role in the creation of polymorphism in the genus <it>Potentilla</it>. However, multiple origin of hybrids and backcrossing are considered to produce a variety of evolutionary spontaneous forms existing aside of reproductively stabilised, established lineages.</p>
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