Karyomorphometric Differentiation and Karyotype Asymmetry in Five Rare Zingiber Species from Thailand

Cytogenetic information remains limited for many rare and geographically restricted species of Zingiber in Thailand. This study investigated chromosome numbers, karyotype characteristics, centromeric-index and relative chromosome-length variation, and karyotype asymmetry in Z. brachystachys, Z. gramineum, Z. mekongense, Z. pellitum, and Z. pyroglossum. Somatic chromosomes were examined from root-tip meristems using the aceto-orcein squash technique, followed by quantitative karyotype analysis, principal component analysis (PCA), UPGMA clustering, and Stebbins asymmetry classification. All five examined taxa had 2n = 22 and NF = 44 but differed in karyotype formula: 8sm + 3st, 3m + 7sm + 1st, 5sm + 6st, 1m + 5sm + 5st, and 7sm + 3st + 1t, respectively. Multivariate analyses incorporating both centromeric index (CI) and relative chromosome length (RL) showed clear karyomorphometric differentiation among the five taxa. UPGMA analysis grouped Z. pellitum and Z. brachystachys most closely, whereas Z. gramineum joined the remaining taxa at the greatest clustering distance. The first two PCA components explained 74.591% of the total variation. Stebbins categories ranged from 3A to 4B. These results provide new comparative cytogenetic data for five rare Thai Zingiber species and demonstrate interspecific variation in chromosome morphology despite uniformity in chromosome number.