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Introduction and objectives: The genus Pilosella is native to Europe and Asia, but its species are successful invaders on most continents. These species form an agamic complex with common apomixis. Apomictic species hybridize and have different degree of residual sexuality. Main aim of this paper was to determine if interspecific hybridization already occurred in Patagonia. M&M: We analysed seed progeny collected at thirteen populations of Pilosella in southern Argentina and Chile. The taxonomic identity of plants, DNA ploidy level (using flow cytometry), chromosome number, reproduction, formation of parthenogenetic seeds and clonal identity (using isozyme phenotypes) were examined. Results: No mixed-species population was recorded. Two apomictic clones of P. officinarum (one pentaploid and the other hexaploid) were found in populations: eight were hexaploid and one was mixed in cytotype composition. A new species for Patagonia, the apomictic pentaploid P. caespitosa, was represented by plants from two Argentinean populations. Some of the progeny plants, cultivated from seeds sampled at three localities, represented seed-fertile aneuploids the morphology of which suggest a hybrid origin with P. officinarum as one of the parental species. Conclusions: The presence of seed-fertile, aneuploid and parthenogenetic hybrids among the cultivated plants signifies an increased risk of the formation of new hybridogeneous genotypes of Pilosella in southern Patagonia. [ABSTRACT FROM AUTHOR]