Variability of the chromosomal number and meiotic behavior in populations ofBidens pilosaL. (Asteraceae) from southern Brazil

Bidens pilosa is a medicinal species from the Asteraceae family, with a wide geographical distribution, found all over Brazil. There are no reports on chromosomal studies from the Brazilian South. Mitotic chromosomes, meiotic behavior, and pollen viability were studied in 6 populations of B. pilosa from Rio Grande do Sul State, Brazil, using conventional staining with acetic orcein 2%. The populations include cytotypes with a variable number of chromosomes: 2n=36, 2n=48 and 2n=54, indicating polyploidy and aneuploidy. The meiotic process was considered regular, even though irregular chromosomal pairing appeared, which is normal in cytotypes from a polyploid complex. The irregularities observed were mainly on univalent, trivalent, and tetravalent pairing associations. However, the pollen viability estimative was high.