| Summary: | How polyploids become established is a long-debated question, especially for autopolyploids that seem to have no evolutionary advantage over their progenitors. The <i>Centaurea aspera</i> polyploid complex includes diploid <i>C. aspera</i> and two related tetraploids <i>C. seridis</i> and <i>C. gentilii</i>. Our purpose was to study the mating system among these three taxa and to analyze its influence on polyploid establishment. The distribution and ploidy level of the Moroccan populations, and forced intra- and inter-specific crosses were assessed. Allotetraploid <i>C. seridis</i> produced more cypselae per capitulum in the intra-specific crosses. It is a bigger plant and autogamous, and previous studies indicated that selfing forces the asymmetric formation of sterile hybrids. All these characteristics help <i>C. seridis</i> to avoid the minority-cytotype-exclusion effect and become established. Inter-specific hybridization was possible between <i>C. aspera</i> and <i>C. gentilii</i>, and with the symmetric formation of hybrids. However, 49% of the hybrid cypselae were empty, which probably reveals postzygotic barriers. Autotetraploid <i>C. gentilii</i> produced the same number of cypselae per capitulum as those of the diploid parental, has an indistinguishable field phenotype, is allogamous, and symmetrically produces hybrids. Therefore, <i>C. gentilii</i> does not seem to have the same competitive advantages as those of <i>C. seridis</i>.<span style="color: windowtext;"></span>
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