This study presents a cytogenetic and comparative analysis of three rare terrestrial orchid species from Thailand: Habenaria janellehayneana, H. rhodocheila, and Nervilia khaoyaica. Somatic chromosome numbers, karyotype structures, and chromosomal morphology were investigated using conventional cytological techniques. The results revealed that both H. janellehayneana and H. rhodocheila possess a chromosome number of 2n = 42 with a fundamental number (NF) of 84, whereas N. khaoyaica has 2n = 36 and NF = 72. Karyotype formulas were determined as 11m + 10sm for H. janellehayneana, 21m for H. rhodocheila, and 2m + 16sm for N. khaoyaica, all indicating symmetrical karyotypes. Multivariate analyses, including Principal Component Analysis (PCA) and hierarchical clustering, were applied to both morphological and karyological datasets. The results demonstrated clear separation between genera along the primary component axis, while species within Habenaria were distinguished along the secondary axis. Karyotype-based PCA further supported distinct chromosomal patterns among all three species, despite identical chromosome numbers in the two Habenaria taxa. This study provides the first cytogenetic report for these species and highlights the importance of chromosome structure, particularly centromere position and arm ratio, in species delimitation. The findings contribute valuable baseline data for taxonomy, evolutionary studies, and conservation of Orchidaceae in Thailand.
Watthana et al. (Sun,) studied this question.
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