Chromosome number, meiotic behavior and pollen fertility of six species of Chrysolaena (Vernonieae, Asteraceae)

Abstract

Chromosome number, meiotic behavior and pollen fertility were determined for six species of the genus Chrysolaena H.Rob. (Vernonieae, Asteraceae). All the species had a base chromosome number of x=10, with somatic numbers that ranged between 2n=20 and 2n=60. The chromosome number of Chrysolaena obovata (Less.) Dematt. (2n=4x=40) and a new cytotype for C. lithospermifolia (Hieron.) H.Rob. (2n=4x=40) are reported for the first time. Normal meiotic behavior was observed for the diploid species C. platensis (Spreng.) H.Rob., C. propinqua (Hieron.) H.Rob. and C. flexuosa (Sims) H.Rob. However, the polyploid taxa C. obovata, C. lithospermifolia (tetraploid) and C. cognata (Less.) Dematt. (hexaploid) showed many meiotic irregularities such as multivalent formation, chromosomes outside plate, early segregation of chromosomes, laggards and bridges in anaphase and telophase. Pollen fertility was high in all species, however, including in the polyploids. Polyploidy is more common in Chrysolaena than in any other New World Vernonieae so far reported and appears to be an important factor in the evolution of this genus.