The Qinghai–Tibetan Plateau is biologically diverse, with 9556 species of vascular plants in the 2,500,000 km2 plateau area. We focused on seed plants from the Qinghai–Tibetan Plateau. A total of 9321 species in the Qinghai–Tibetan Plateau were recorded. Sixty-one of these genera are Chinese endemics. Our results suggested that the flora of the Qinghai–Tibetan Plateau was charac- terized by relatively few polyploids, and aneuploidy was also considered as relatively rare. We inferred that aneu- ploidy may be affected by environmental factors and the addition or loss of centromeres. Furthermore, the highest frequency of polyploids was found among perennial herbs. Annuals had low polyploidy, and perennials had high polyploidy. Species richness was correlated with the inci- dence of polyploids, environmental conditions, and repro- ductive isolation.