Cytotaxonomic studies in six species ofVernonia(Asteraceae: Vernonieae)

Abstract

Abstract In this report, we describe a mitotic analysis (Giemsa technique) of six species of the genus Vernonia sensu Baker (Asteraceae, Vernonieae, section Lepidaploa) in order to assess the validity of maintaining this genus (sensu Baker) or dividing it into several lesser genera (sensu Robinson). Specimens of the seven species were collected in “cerrado” and “campo rupestre” areas in the states of São Paulo, Minas Gerais and Goiás. The chromosomal numbers (2n=32 and 2n=34) and karyotypes revealed a predominance of metacentric chromosomes, with some sub-metacentrics. The chromosome sizes varied from 1.2 to 4.9 μm, the total chromatin length (TCL) ranged from 31.3 to 50.7, and the asymmetry index TF% ranged from 42.3 to 44.4. The intrachromosomal asymmetry index (A1) varied from 0.15 to 0.19, while the interchromosomal asymmetry index (A2) ranged from 0.14 to 0.21. A dispersion diagram showed that population 1 of V. polyanthes had the most asymmetrical karyotype. These results still do not allow a comprehensive and conclusive cytotaxonomic discussion of this group, mainly because of the lack of a characteristic or standard karyotype for most infrageneric groupings (sections and subsections) and also because most species have not yet been analyzed cytogenetically. Nevertheless, the available data indicate only a tenuous relationship between the chromosome numbers observed here and reported in the literature compared to the taxonomic reorganization of the genera Lessingianthus, Vernonanthura and Chrysolaena proposed by Robinson.