SUMMARY The species Senecio aetnensis Jan., S. joppensis Dinsm., S. squalidus L., S. viscosus L. and S. vulgaris L. have been compared for automatic selfing ability, capitulum conspicuousness, pollen yield, chromosome number and chiasma frequency. It has been established that the species S. aetnensis, S. joppensis and S. squalidus which have low automatic selfing ability have large, showy capitula, high pollen output and low recombination indices. The species S. viscosus and S. vulgaris which have a high selfing ability have relatively inconspicuous capitula, low pollen yields and a high recombination index. The differences in recombination index values are mainly due to the fact that the selfing species are polyploids but it may be significant that the highest average chiasma frequencies per bivalent were found in some S. vulgaris plants. The adaptive significance of a high recombination index in inbreeding taxa is discussed and it is suggested that a high chiasma frequency and/or polyploidy may have a preadaptive value in facilitating the change from outbreeding to inbreeding in some species.

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