I review the cytology of the Senecioneae, with emphasis on North American genera and in the context of our developing knowledge of phylogenetic relationships from cladistic analyses of morphological and, especially, DNA data. Most information is from recent cladistic analyses, cytological summaries, and discussions by other workers, but 31 new counts representing 20 species in 11 genera (Mexican Arnoglossum, Pittocaulon, Ligularia, Psacalium, Roldana, Senecio and Telanthophora, as well as Emilia, Erechtites, Gynura, Kleinia and Senecio from elsewhere) are presented, with pictures of representative habitats, species, and chromosomal preparations. The base number of the tribe is most likely x = 10, which some phylogenies suggest, e.g., where the tribe is sister to the Calenduleae (x = 10) and where this clade is sister to the Inuleae (x = 10 or 9) which is itself sister to the Astereae/Anthemideae clade (x = 9) -- indicating aneuploid reduction from x = 10 to x = 9 in these latter clades. However, a recent phylogeny is ambiguous, with different outgroups of the Senecioneae having x = 10 or x = 9 -- or 8 or 7. The x = 9 of the most basal of the three (or four) subtribes in the Senecioneae, the Blennospermatinae (and Abrotanellinae) is most likely derived by aneuploid reduction. The largest subtribes, the Senecioninae and Tussillaginae, which are apparently sister groups and with x = 10 and x = 30, respectively, probably both arise from an ancestral x = 10, with the hexaploid x = 30 being fixed early in the latter clade. Polyploidy (especially in the former subtribe) and aneuploidy (in both) give numbers, most of which fit neatly into this scenario, but some of which have obscure origins or are superficially discrepant.

Key words: Asteraceae, chromosome numbers, cytological evolution, cytology, phylogeny, Senecioneae