Chromosome numbers in the aureoid Senecio complex (Asteraceae)

Abstract

Chromosome numbers are reported for 12 species of the aureoid Senecio complex. First reports are presented for Senecio debilis (n = 23) and Senecio crocatus (n = 23) and a new report is presented for Senecio dimorphophyllus (n = 23). Polyploidy is common in the widespread species of the complex, but in all cases diploid populations are still extant. In Senecio neomexicanus, polyploidy is correlated with infraspecific variation at the varietal level. In Senecio pauperculus, the distribution of tetraploid populations is correlated with previously glaciated regions. Tetraploid populations of Senecio streptanthifolius are of two distinct types, a northern race resembling diploid populations from the same area and a southern race of possible alloploid origin. All species examined contained at least some diploid populations.