Chromosome studies in the genus Mikania (Asteraceae)

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Mikania is the largest genus of the tribe Eupatorieaewith about 430 species distributed in the pantropics, tem-perate America, and Southern Africa, but with its two majordiversity centers in the highlands of southeastern Brazil andthe eastern foothills of the Andes from Bolivia to Colom-bia (King and Robinson, 1987; Holmes, 1995). The genusis widely distributed in Brazil with about 200 described spe-cies (Barroso, 1958, 1986), many of which are endemic tosouthern Brazil, but with a greater number of species beingfound in Amazon region.The species are characterized by their capitula whichis composed of four florets and an involucre composed offour phyllaries that is subtended by a subinvolucral bract.There is no variation from this basic organization, and spe-cific differences mostly involve the type of capitulescence,size of habit, shape of organs, and plant texture (Holmes,1995).Until 1987 chromosome studies of the genus havebeen limited to chromosome counts, but such counts areavailable for only about 10% of the species (Gaiser, 1954;Mangenot and Mangenot, 1958; Turner, 1962; Turner et al. ,1967; Baquar, 1967-1968; Mitra and Datta, 1967; Sharmaand Sakar, 1967-1968; Coleman, 1968; Nevlin, 1969;Powell and King, 1969; King et al., 1976; Turner et al.,1979; Nauman, 1981; Mathew and Mathew, 1983; Strother,1983; Waisman et al. , 1984).The first karyotype studies in Mikania were made byRuas and Ruas (1987) on six species from which they sug-gested that there was an evolutionary trend in the genus to-wards the formation of aneuploid and polyploid series. In astudy of ten species of Mikania Ruas (1989) and Ruas andAguiar-Perecin (1997) proposed a correlation betweenmorphological and chromosomal evolution, while an analy-sis of 12 cytotypes of Mikania micrantha by Maffei (1996)showed that the same evolutionary mechanisms that occuramong species also occur at intraspecific level, results alsoseen in a study of two populations of M. cordifolia by Maffeiet al. (1999a).In this review, the chromosomal evolution of the ge-nus Mikania is discussed based on currently available data.