Karyotype of five Astragalus species from the alpine subnival belt in the Hengduan Mountains

The chromosome numbers and karyotypes of five species of Astragalus (Fabaceae) collected from the alpine subnival belt in the Hengduan Mountains were determined. All species were analyzed by conventional staining and pressing methods. The karyotype formulae of the five species are reported for the first time. Results showed that: A. craibianus Simps., A. acaulis Baker, A. ernestii Comb., A. tongolensis Ulbr. were diploid, while A. degensis Ulbr. was tetraploid. The chromosome base number for all studied species was x = 8. The karyotype formula of A. craibianus was 2n = 2x = 16 = 6sm + 10m, 2A. The karyotype formula of A. acaulis was 2n = 2x = 16 = 2sm + 14m, 2A. The karyotype formula of A. ernestii was 2n = 2x = 16 = 2sm + 14m, 2A. The karyotype formula of A. degensis was 2n = 4x = 32 = 4sm + 28m, 1A. The karyotype formula of A. tongolensis was 2n = 2x = 16 = 2st + 2sm + 12m, 2A. All species of Astragalus in the Hengduan Mountains were previously reported to be diploid, but this study discovered a tetraploid species for the first time. These results not only expand basic information on the chromosomes of legumes in the alpine subnival belt of the Hengduan Mountains, but also provide a cytological reference for the study of plant phylogeny and evolution of plants within Astragalus in this region.