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Sixteen species of Jaborosa (Solanaceae), including eight endemic to Argentina, were studied karyologically. The numbers n = 12 and/or 2n = 24 were found in all species, the majority of the cases being new reports. Mitotic chromosomes were small- to medium-sized, the average length varying from 2.95 to 4.93 µm. All species had one to three chromosome pairs with satellites. The karyotypes, obtained for 13 species, were slightly asymmetrical: A1 ranged from 0.228 to 0.483, A2 ranged from 0.095 to 0.182, and Paszko's asymmetry index ranged from 0.84 to 3.47. In all species, metacentric chromosomes were the most common, followed by submetacentrics, but subtelocentrics were rare. Morphological similarities and sectional arrangements were not reflected in either a principal components analysis plot or asymmetry index plot, but the species could be singled out by their karyotype formulae and the different karyotype parameters taken. In Jaborosa, a notably diversified genus, exo-morphological evolution has taken place, together with evident chromosome rearrangements, whose disposition is different and not as clear as in related genera. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 156, 467–478. [ABSTRACT FROM AUTHOR]