Cytotaxonomy of species of Vernonia, section Lepidaploa, group Axilliflorae (Asteraceae, Vernonieae)

Abstract

Mitotic chromosomes of eight populations of six species of Vernonia sensu Baker (Asteraceae, Vernonieae, section Lepidaploa , group Axilliflorae ) were studied to assess the validity of maintaining the genus as proposed currently ( sensu Baker) or of splitting it into several smaller genera ( sensu Robinson). The species were collected in areas of 'cerrado' and 'campo rupestre' in southern and central-western Brazil. The chromosome numbers were 2 n = 20-40 and karyotypic analysis showed a predominance of metacentric chromosomes, with some submetacentrics. B chromosomes were seen in one population of V. geminata . The chromosomes varied in length from 0.9 to 4.6 µ m, with a total chromatin length of 29.7-45.0 µ m and a symmetry index of 41.2-46.9%. The intrachromosomal asymmetry index varied from 0.13 to 0.29, and the interchromosomal asymmetry index varied from 0.15 to 0.21. The dispersion diagram showed that population 1 of V. geminata had the most asymmetrical karyotype. These results do not provide sufficient evidence for a conclusive cytotaxonomic discussion of Vernonia , mainly because of the impossibility of associating any infrageneric group with specific karyotypic characters, and also because of the small number of species analysed so far.

Karyotype characterization of two populations of Vernonia geminata (Asteraceae, Vernonieae) using banding and FISH techniques

“…We analyzed the same populations of V. geminata studied by Oliveira et al (2007a), collected in disturbed area, in Analândia, São Paulo State, Brazil. The population 1 occurred in an urban area and the population 2 in an open-pasture area, about 15 km away.…”

“…Chromosome numbers of only 20% of Vernonia have been reported, varying from 2n = 18 to 160 (Oliveira et al, 2007a). The karyotypes determined with conventional techniques include only 5% of the species of Vernonia, and they do not discriminate very well species with the same chromosome number, due to small variation in chromosome size and centromeric position (Ruas et al, 1991;Dematteis, 1996Dematteis, , 1998Fernández, 1998, 2000;Oliveira et al, 2007a,b).…”

“…V. geminata has 2n = 20 chromosomes predominantly metacentric, varying from 2.0 to 4.6 µm. Oliveira et al (2007a) reported the occurrence of B chromosomes (0-6) in one population of this species.…”

“…It is an important honey species, where its pollen is detected in the honey and the larval food of Tetragonisca angustula Latreille, a bee species found in Chiapas, Mexico (Martínez-Hernán-dez et al, 1994). Karyotypes of V. geminata and other species of Vernonia have been described by Oliveira et al (2007a) by conventional staining. V. geminata has 2n = 20 chromosomes predominantly metacentric, varying from 2.0 to 4.6 µm.…”

“…Cass., occurs from Mexico to South America (Jorgensen and Ulloa, 1994), including the "cerrado" (Oliveira et al, 2007a) and disturbed areas in Brazil. It is an important honey species, where its pollen is detected in the honey and the larval food of Tetragonisca angustula Latreille, a bee species found in Chiapas, Mexico (Martínez-Hernán-dez et al, 1994).…”