Overview of Cytogenetics in the Subtribe Orchidinae (Orchidaceae) in the Mediterranean Region

In the Mediterranean region, for over 150 species belonging to the subtribe Orchidinae, chromosome number has been documented and found to range from 2n = 32 to 2n = 42. This work renews and updates chromosome numbers and reports a karyomorphological comparison between species with 32 or 36 chromosomes and species with 40 or 42 chromosomes. Notably, in the 32,36-chromosome group, species within the genus Anacamptis s.l. show substantially similar karyomorphology, although some species exhibit differences in chromosome structure and heterochromatin distribution. In contrast, in the 40,42-chromosome group, the chromosomes are comparatively smaller and therefore difficult to sort into karyotypes when standard staining techniques are used. However, the two groups display distinct heterochromatin patterns, particularly in centromeric and telomeric regions. Given the growing body of information in this field, a review of current cytogenetic knowledge is warranted. In this report, the authors present classical and molecular cytogenetic data and highlight important aspects of karyotypic evolution in Orchidinae. Traditional karyotypic analysis, based on stained mitotic chromosomes, can be used to distinguish and identify taxonomic groups. Karyomorphometric studies in particular reveal subtle differences between closely related chromosome sets within Orchidinae. Furthermore, wide variation among genera in terms of heterochromatin content was observed. Further comparative data between the two above-mentioned groups are summarized.