Karyotype analysis in someVernoniaspecies (Asteraceae) from South America

SUMMARYThe somatic chromosomes of eight Vernonia species (Asteraceae) from Brazil, Paraguay and Argentina were analyzed. First chromosome counts are presented for V. coriacea Less. (2n=32 = 20m + 10sm + 2st), V. dura Mart, ex DC. (2n=32 = 22m + 10sm), V. eriolepis Gardn. (2n=32 = 22m + 8sm + 2st), V. grandiflora Less. (2n=64 = 50m + 14sm) and V. onopordioides Baker (2n=32 = 18m + 2m-sm + 10sm + 2st). Besides, the chromosome numbers of V. brevifolia Less. ((2n=32 = 22m + 10sm) and V. sellowii Less. (2n=62 = 40m + 20sm + 2st) are also confirmed. The number found in V. saltensis Hieron (2n=64 = 48m + 16sm) support the occurrence of two cytotypes within the species, one diploid (2n=32) and the other tetraploid (2n=64). The eight species revealed certain differences between their karyotypes principally in formula, total length and asymmetry level, which coincides with earlier studies for South American taxa. Satellites were commonly found on submetacentric or subtelocentric pairs, being also variable in morphology and location. Chromosomal data here reported and the already available for the genus indicate that the evolution of Vernonia have been followed for a decrease in number and size of the chromosomes.