Karyotype analysis in eight species of Vernonia (Vernonieae, Asteraceae) from South America

Abstract

The somatic chromosome number and karyotype of eight species of Vernonia were analyzed. The results include the first chromosome count for Vernonia hexantha Sch. Bip. (2n=30), wich is diploid with a base number x=15. The karyotypes are analyzed for the first time for two cytotypes of V. cognata Less. (2n=40=28m + 12 sm; 2n=80= 48m + 32 sm), V. hexantha (2n=30=24m + 6sm); V. membranacea Gardner (2n=34=24m + 10sm); V. salzmanii DC. (2n=20=10m + 10sm) and V. verbascifolia Less. (2n=20=12m + 8sm). All the studied species showed a predominance of metacentric chromosomes, with a lower proportion of submetacentric pairs. In V. brevifolius Less. 0 to 3 accesory or B chromosomes were found. The chromosome varying in length from 1.25 to 3.98 µm. The differences in the symmety of the karyotypes were small, from which its possible to assume that the great diversification of the genus has been acompained by very small changes in the structure of the chromosomes.