Abstract: The seeds of three endemic plants collected from the Qinghai-Tibet Plateau and germinated on wet filter papers and root tip-squash method were used for cytological observation.The results showed that three species were diploid. Chromosome numbers of all 5 populations of Micranthes melanocentra were 2n=22; chromosome numbers of 2 populations of Micranthes atrata were 2n=22. All 5 populations of Swertia przewalskii had same chromosome numbers, the karyotype formula was 2n=24=20m+4sm, 1B,As. K%=58.8%. The third and ninth pairs were submetacentric, and the rest were metacentric. The chromosome cardinality of Micranthes melanocentra was consistent with previous studies, but no polyploid was found, indicating that the polyploid frequency was low in the sampling area. The karyotypes of Micranthes atrata and Swertia przewalskii were reported for the first time. The reported karyotypes of the three plants complemented the cytological data of the species endemic to the Qinghai-Tibet Plateau, and provided cytological data for the development, utilization and conservation of these species.

Key words: Qinghai-Tibet Plateau, karyotype, Saxifraga, Swertia, endemic plants