Cytogenetic Diversity in Orchis s.i. and Allied Genera (Orchidinae, Orchidaceae)

Cytogenetic relationships among species of genus Orchis s.l. and allied genera are considered. Chromosome numbers and karyotype structure of numerous taxa are compared based on Feulgen, Giemsa C-banding, and DAPI (4’-6-diamidino-2-phenylindole) stained somatic metaphase chromosomes. The fundamental diploid numbers observed were 2n = 36, 40, and 42. Analyses indicated that chromosome complements differed markedly in chromosome size and karyotype structure. The amount and distribution of constitutive heterochromatin varied considerably among the taxa studied; in some cases a correlation was found between asymmetrical karyotype and heterochromatin content. In some species DAPI staining revealed that most heterochromatin regions are rich in A-T base pairs. The 18S, 5.8S-25S (pTa71) and 5S (pTa794) r DNA were used in Anacamptis s.l. and Steveniella-Himantoglossum s.l. species as probes for in-situ hybridization to reveal localization of ribosomal genes. Our results seem to indicate that both karyomorphology and heterochromatin distribution are a major cause for a possible evolutionary pathway. Chromosomal rearrangements and evolutionary trends in representative genera of subtribe Orchidinae are discussed.