Molecular cytogenetic insights into the evolution of the epiphytic genus L epismium ( C actaceae) and related genera

Changes in chromosome structure and number play an important role in plant evolution. This was investigated in the N eotropical epiphytic cacti: all L epismium spp. and some related R hipsalis spp . Both genera have species with disjunct distributions between the paranas of south‐eastern B razil and north‐eastern A rgentina and the yungas forests of the eastern A ndes. K aryotypes, fluorescent banding and fluorescence in situ hybridization ( FISH ) studies using rDNA probes were performed. A time‐calibrated phylogenetic tree was generated to place the karyological information and biogeographical history in an explicit evolutionary context. All species were 2 n  = 22 and showed symmetrical karyotypes comprising only metacentric chromosomes of similar sizes. The heterochromatin bands were always associated with chromosome satellites coinciding with the location and number of the 18 S –5.8 S –26 S rDNA loci. The 5 S rDNA loci had more heterogeneous profiles with one or two loci per haploid genome. Phylogenetic analysis suggested an ancient duplication event of the 5 S rDNA loci and more recent post‐speciation translocation and deletion events. These genome restructurings are estimated to have occurred approximately 13.98 Mya in the middle M iocene, after L epismium and R hipsalis diverged. The ancestor of L epismium may have had a similar karyotype to L . lumbricoides and the R hipsalis spp. (i.e. one 5 S locus on chromosome 2). Both genera hypothetically originated in the yungas (north‐eastern A rgentina and southern B olivia), but diversification of the L epismium crown group probably originated from populations with duplicated 5S loci in the parana forests of south‐eastern B razil (8.70 Mya in the late M iocene). Two migration events between the yungas and parana forests were suggested to explain the extant distribution of L epismium spp. These results make Lepismium a model system for the study of the complex chromosomal evolution in plants. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society , 2015, 177 , 263–277.