Número de cromosomas, anomalías meióticas y formación de polen 2n en accesiones de la especie silvestre Chrysolaena flexuosa (Vernonieae, Compositae) de su rango de distribución en Argentina.

Chrysolaena flexuosa is a South American species of potential ornamental value (basic chromosome number of x=10). Diploid (n=10) and tetraploid (n=20) cytotypes have been reported for its distribution area, although one hexaploid (n=30-32ca.) cytotype has been reported for its most southern distribution. To investigate if ploidy and latitude are positively related in Ch. flexuosa natural populations and if sexual polyploidization could have had a role in the origin of the polyploid cytotypes, we determined chromosome numbers, DNA content, and pollen viability and size, and analyzed microsporogenesis in samples of seven Argentinian accessions. Two of the northeastern accessions were diploid and one was tetraploid, whereas the four southeastern accessions were hexaploid. Ploidy levels determined both by chromosome countings and flow cytometry coincided, although monoploid genome size significantly decreased with increasing ploidy. In all accessions, variability was observed for pollen viability and size, as well as for large (presumably 2n) pollen production. This variability was underlined by abnormal cytological events in meiosis and at the tetrad stage (lagging chromosomes, parallel spindles, triads). The results would indicate that there is, apparently, a positive relation between ploidy and latitude, and suggest a likely role of sexual polyploidization in the origin, establishment and expansion of Ch. flexuosa populations.