Karyotypes and chromosome morphology in the genus Mikania (Compositae). I.

Abstract

The genus Mikania, which belongs to the tribe Eupatorieae of the family Compositae , is a group of herbaceous plants comprising about 300 species distributed in the tropical and sub tropical areas of the American continent and Asia . Barroso (1958) has found 150 species of Mikania distributed along all the Brazilian regions , many of those species being endemic.No karyological studies of this genus are available , and in some species only chromosome number has been recorded (Mitra 1947, Gaiser 1954, Mangenot and Mangenot 1958 , 1962, Turner et al. 1962. Mitra and Datta 1967, Turner et al. 1967, Baquar 1967-1968 , Sharma and Sakar 1967-1968, Coleman 1968, Nevling 1969, Powell and King 1969, King et al . 1976, Turner et al. 1979, Nauman 1981, Mathew and Mathew 1983Strother 1983 andWaisman et al. 1984). The present paper gives a detailed karyomorphological study of six species of the genus Mikania. ResultsThe karyotype of six species are presented in Fig. 1. The chromosomes are classified in two groups on the basis of the secondary constriction.The first group consisted on one pair of chromosomes with a secondary constriction in the long arm of the longest pair in the com plement. This was observed in M. cordifolia, M. glomerata, M. laevigata, M. trinervis and M. viminea. M. micrantha has two pairs of chromosomes with a secondary constriction in the long arm. The second group consisted of chromosomes without a secondary constriction. In each group the chromosomes were classified in M, m, sm and st, following the nomenclature of

Chromosome studies in the genus Mikania (Asteraceae)

“…Thirty-two taxa of Mikania have so far been examined, including 16 different species (Ruas and Ruas, 1987;Ruas, 1989;Ruas and Aguiar-Perecin, 1997), 14 populations of M. micrantha (Ruas and Ruas, 1987;Maffei, 1996;Maffei et al, 1998Maffei et al, , 1999b and two populations of M. cordifolia (Ruas and Ruas, 1987;Maffei et al, 1999a). All the karyotypes were characterized by the presence of a secondary constriction in the long arm of chromosome 1, and Ruas and Ruas (1987), in the analysis of six species, proposed that this secondary constriction should be considered a cytological marker for the genus.…”

“…The first karyotype studies in Mikania were made by Ruas and Ruas (1987) on six species from which they suggested that there was an evolutionary trend in the genus towards the formation of aneuploid and polyploid series. In a study of ten species of Mikania Ruas (1989) and Ruas and Aguiar-Perecin (1997) proposed a correlation between morphological and chromosomal evolution, while an analysis of 12 cytotypes of Mikania micrantha by Maffei (1996) showed that the same evolutionary mechanisms that occur among species also occur at intraspecific level, results also seen in a study of two populations of M. cordifolia by Maffei et al (1999a).…”

Numerical chromosome polymorphism in Mikania cordifolia Willd. (Asteraceae)

“…Previous karyotypic descriptions for this species showed a numerical chromosome variation of 2n = 34 to 38 (Gaiser, 1954;Powell and King, 1969;Ruas and Ruas 1987;Robinson et al, 1989). Numerical polymorphism is relatively common for some plant species.…”

“…There is not much cytogenetical information about this genus, and most concerns only chromosome number. In Mikania cordifolia, chromosome number has been reported as 2n = 38 (Gaiser, 1954); n = 18 (Powell and King, 1969), n = 19 (Robinson et al, 1989) and 2n = 34 chromosomes (Ruas and Ruas 1987). The objective of the present study was to characterize the chromosome number and morphology of an M. cordifolia population from Campinas, São Paulo (southeastern Brazil).…”

“…Based on our analysis, we suggest that aneuploidy has an important role in the evolution of M. cordifolia. Ruas and Ruas (1987) suggested that the secondary constriction in the biggest arm of chromosome one is a cytological marker for this genus. We confirm the presence of this marker.…”