Chromosomal evolution in P leurothallidinae ( O rchidaceae: E pidendroideae) with an emphasis on the genus A cianthera : chromosome numbers and heterochromatin

In this study, we analysed chromosome number variation and chromomycin A 3 /4′,6‐diamidino‐2‐phenylindole ( CMA / DAPI ) banding patterns in 48 species belonging to 12 genera of subtribe P leurothallidinae ( O rchidaceae) in order to understand the chromosome evolution based on recent phylogenetic hypotheses and taxonomic treatments. All species had small chromosomes, with numbers ranging from 2 n  = 20 in two Specklinia spp. to 2 n  = 80 in an unidentified O ctomeria sp. In A cianthera , the most highly represented genus in this study, a great diversity of chromosome number and pattern of fluorescent bands was observed, showing heterochromatin accumulation in A cianthera section S icariae subsection P ectinatae . Interspecific ascending and, mainly, descending dysploidy were the main mechanisms of chromosome number evolution in subtribe P leurothallidinae. For P leurothallidinae, x  = 20 is suggested as the basic chromosome number, the same suggested for the related subtribe Laeliinae and for the whole tribe E pidendreae. The B razilian species of the mega‐genus S telis had chromosomes with small amounts of heterochromatin and chromosome numbers based on x 2  = 16. These are generally divergent from those reported for A ndean and M eso‐ A merican species, but in agreement with the monophyletic hypothesis proposed for S telis spp. with a Brazilian Atlantic distribution. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 178 , 102–120.