Karyotype analysis of Cosmos bipinnatus

In order to provide necessary cytology information on germplasm identification, origin analysis, species succession and breeding, the chromosome number and karyotype of Cosmos bipinnatus were studied. The results showed that the chromosome number of C. bipinnatus was 2n=24, and its karyotype formula was 2n=2x=24=18m (1sat)+6sm (1sat). The average relative length of chromosomes was 6.20% to 9.06%. Ratio of the longest to the shortest chromosome was 1.47%，16.7% of chromosomes showed long arm/short arm2∶1. The karyotype of C.bipinnatus belongs to 2A type. As the asymmetry coefficient was 43.25%, chromosome of C.bipinnatus should be a more symmetric type.