Karyotypes and Chromosome Morphology in the Genus Mikania (Compositae) I

Abstract

Karyotypes from six species of genus Mikania were studied utilizing root tip metaphase mitoses. Two species were diploid with 2n=36, M. cordifolia was diploid with 2n=34, M. laevigata, was diploid with 2n=38, M. micrantha and M. viminea were tetraploid with 2n=72 and 2n=68, respectively. Five out of the six species analysed had one pair of a comparatively long chromosome with a secondary constriction in the long arms, and one species (M. micrantha) had two pairs of such long chromosomes. The basic chromosome number of this genus is 18, and we suggest that there is an evolutionary trend towards formation of aneuploid series and polyploidy.