Karyotype Analysis in Some Genera of Compositae

V. The chromosomes of American Aster species

Abstract

1. The karyotypes of 15 species of American species of Aster are reported.
2. The chromosome numbers of 9 species are reported here for the first time. These are: A. modestus 2=18; A. puniceus 2n=16; A. concinus 2n=46; A. pilosus 2n=48; A. simplex 2n=64; A. chilensis 2n=64; A. exilis 2n=10; A. occidentalis 2n=16; A. alpigenus 2n=18.
3. The primitive basic chromosome number for the genus is considered to be 9.
4. Judging from the chromosome numbers and the karyotypes the origin of this polyphyletic genus is probable in the American species of Aster.
5. In strong contrast to the symmetrical karyotype of Asiatic species of asters, there is a marked increase in asymmetry in the karyotype of the American species.
6. In general the chromosomes of the New World taxa are smaller than those of the Old World species.