Polyploidy in Two Species of the Allium ampeloprasum Complex (Amaryllidaceae): New Evidence and Cytogenetic Insights

Providing new cytogenetic results, this study analyzes the karyotype of Allium polyanthum and A. atroviolaceum (Amaryllidaceae sect. Allium) using classical cytogenetic techniques (Feulgen staining, Ag-NOR, C-banding), while explicitly excluding meiotic analyses. Both species show a stable tetraploid chromosome complement (2n = 4x = 32) across all examined populations, with predominantly symmetrical karyotypes dominated by metacentric chromosomes; quantitative asymmetry parameters (MCA, CVCL, CVCI) are very similar between the two species. Notably, a single specimen of A. atroviolaceum from Albania represented an exception: the chromosome number was variable within the meristematic tissue, exhibiting somatic numerical instability. The main differences concern the organization of nucleolar chromosomes: both species show secondary constrictions in a sub-telomeric position (i.e., “scorodoprasum” type) and secondary constrictions near the centromere (i.e., “sativum” type), but with different numbers and distributions. Allium polyanthum shows a maximum of 4 nucleoli per interphase nucleus (corresponding to 2 pairs of homologous chromosomes with secondary constrictions), while A. atroviolaceum shows up to 7, often smaller in size. The distribution of constitutive heterochromatin (C-banding) is also species-specific, despite an overall similarity in chromosome morphology. The authors interpret these features (normal chromosomal rearrangement, karyotype symmetry, heterochromatin organization) as indicative of a relatively recent evolutionary event, which may have contributed to the cytogenetic stabilization and diversification of these taxa. The study also confirms the usefulness of conventional cytogenetic markers, when integrated with NOR and heterochromatin analysis, for studying chromosome evolution in polyploid species of the genus Allium.