Telomeric repeat distribution and chromosomal evolution in the slipper orchid genus Paphiopedilum

The chromosomal mechanisms responsible for the extraordinary diversity in chromosome number and karyotype structure in Paphiopedilum remain incompletely resolved, particularly the processes by which extensive dysploid variation has arisen in the apparent absence of polyploidy. Telomeric repeats provide informative cytogenetic markers for reconstructing chromosome evolution because their typically terminal localization and repetitive nature can retain signatures of breakage, fusion, and repair. To address the chromosomal evolutionary problem in Paphiopedilum, telomeric repeat distribution was examined in 41 species representing all major taxonomic sections (phylogenetic lineages) using fluorescence in situ hybridization (FISH). In addition to conventional terminal telomeres, diverse interstitial telomeric repeat (ITR) patterns were detected, including centromeric, pericentromeric, and subtelomeric arrays, as well as rare chromosome ends lacking detectable telomeric signals. Classification of these patterns into twelve chromosomal types, interpreted in a phylogenetic context, suggests that telomere-associated and chromosome structural processes have contributed to karyotype diversification, including centric fission, subtelomeric rearrangement, repeat amplification, and potentially centric fusion, with different processes predominating among lineages. In some sections, such as Pardalopetalum, these types resolve into internally consistent patterns often dominated by terminal localization with recurrent subtelomeric expansion, providing a clear cytogenetic signature of lineage-specific telomere repeat dynamics, whereas other sections exhibit greater within-section heterogeneity in both signal position and intensity. These results provide a coherent cytogenetic framework for dysploid chromosome evolution in Paphiopedilum and identify telomeric repeat dynamics as an important contributor to karyotype diversification in the genus.