The Genome Sizes of Fourteen Wild Paeonia Species Were Systematically Determined for the First Time

China is recognized as one of the global distribution centers for the genus Paeonia . However, among wild peony species, only Paeonia lactiflora has been relatively well-studied and utilized, while other wild peony resources remain under-investigated. In particular, the genome sizes of wild Chinese peonies have not been clearly defined. Among these, P. mairei , an endemic species in China, is classified as Near Threatened on the 2004 China Species Red List due to its limited and valuable wild populations. Nevertheless, its ploidy level and genome size remain unresolved, significantly hindering the further development and application of wild peony resources. In this study, eight populations of P. mairei and 13 additional wild peony species were analyzed using flow cytometry to determine ploidy levels and estimate genome sizes. All eight populations of P. mairei were confirmed as tetraploid, with no diploid types detected. The genome sizes of P. mairei ranged from 21.11 to 25.27 Gb, this study examined the relationship between pronounced variation in genome size among geographically distinct populations and their habitat conditions. The genome sizes of the 13 wild peony species were determined as follows: P. tenuifolia : 9.21 Gb; P. anomala : 9.91 Gb; P. emodi : 10.02 Gb; P. intermedia : 10.75 Gb; P. mlokosewitschii : 11.49 Gb; P. daurica : 11.77 Gb; P. lactiflora : 11.86 Gb; P. veitchii : 12.24 Gb; P. parnassica : 12.72 Gb; P. obovata : 13.51 Gb; P. sterniana : 13.24 Gb; P. officinalis : 18.66 Gb; P. arietina : 23.24 Gb. The study provides the first comprehensive measurements of genome sizes across 14 wild peony species, thereby enriching the genomic repository of the genus Paeonia and establishing a critical foundation for future research in genomics and molecular cytogenetics within this taxon.