Intraspecific Karyotypic Differentiation in the Lycoris aurea Complex Revealed by Fluorochrome Banding and rDNA Fluorescence in situ Hybridization

The Lycoris aurea (L’Hér.) Herb. complex—valued for its medicinal properties and horticultural applications—is characterized by extensive intraspecific dysploidy. However, a comprehensive molecular cytogenetic framework elucidating intraspecific karyotypic differentiation and the underlying evolutionary mechanisms has yet to be established. By integrating fluorochrome banding with 5S and 45S rDNA fluorescence in situ hybridization (FISH), we performed a comparative molecular cytogenetic karyotyping of 20 natural populations spanning 13 provinces in China and synthesized these results with previously published cytogenetic data to conduct a rigorous cytogeographic assessment of this species. Three distinct cytotypes were identified: cytotype A (2n = 14 = 8m + 6t/st), cytotype B (2n = 15 = 7m + 8t/st), and cytotype C (2n = 16 = 6m + 10t/st). Both multivariate karyomorphometric analyses and comparison of DAPI banding and rDNA FISH patterns revealed minimal inter-population karyotypic variation in cytotype A but pronounced intra-cytotypic karyotypic polymorphism in cytotype C. Integrated cytogenetic evidence supports Robertsonian translocation as the primary mechanism driving dysploidy in the L. aurea complex: cytotype C is inferred as the ancestral karyotype, from which cytotype A arose through double Robertsonian fusions and cytotype B through a single such fusion, establishing two parallel, evolutionarily independent lineages. The parapatric partitioning of the three cytotypes is interpreted as the outcome of synergistic effects among Quaternary climatic oscillations, topographic barriers, and ecological niche divergence.