Cytogenetics of Genus Vernonia Schreber (Compositae).

Karyotypes from five species of the genus Vernonia were studied utilizing root tip mitotic metaphases. Vernonia nudiflora and V. polyanthes were tetraploid with 2n=34 (X=17); V. flexuosa and V. simplex were tetraploid with 2n=40 (X=10). V. polyphylla with 2n=64 may be an allotetraploid with X=16 or an autoplolyploid with X=8, that became fertile by diploidization. The basic chromosome numbers are a series of X=7, 8, 9, 10, 15, 16, 17 and 19. We suggest that in Vernonia there is an evolutionary trend towards formation of aneuploid series and polyploidy.