Advances in the Study of Orchidinae Subtribe (Orchidaceae) Species with 40,42-Chromosomes in the Mediterranean Region

This study presents an updated analysis of cytogenetic data for several species within the 40,42-chromosome genera of the subtribe Orchidinae. The research includes insights into the distribution of heterochromatin obtained using C-banding and fluorochrome techniques. Our investigation confirmed variation in the distribution of heterochromatin and repetitive DNA sequences among species pertaining to Neotinea s.l. and Orchis s.str. These variations also potentially contribute to the diversification of these species. Cytogenetic analyses of the Neotinea group demonstrated that both H33258 and DAPI staining result in blocks of fluorescent regions on numerous chromosomes. Particular attention was paid to the cytological composition of the polyploid Neotinea commutata, focusing on its potential origin. Based on the karyological results acquired, a hypothesis concerning the origin of N. commutata is proposed. The most noteworthy revelations regard the O. mascula complex. In these species, the telomeric areas of all chromosome sets display extensive heterochromatin. Fluorochrome staining revealed telomeric blocks on many chromosomes that were not seen with Giemsa staining. This highlighted a distinct feature of O. mascula, where particularly large C-bands surrounding the centromeric regions of multiple chromosomes were found. However, in O. mascula, O. provincialis, O. pauciflora, and O. patens, C+ chromatin may not show a significant response to fluorochrome Hoechst or DAPI+ staining. The unique cytomorphological arrangement observed in the O. mascula species, unlike other members of the O. mascula complex, suggest epigenetic phenomena. Additional data are presented for the genera Dactylorhiza and Gymnadenia. A deeper understanding of the diversity of chromosomal structures among these orchids promises to shed light on the mechanisms underlying speciation, adaptation, and the remarkable diversity characteristic of the Orchidaceae family.