Résumé
The impact of the widespread occurrence of polyploidisation anddescending dysploidy on lineage diversification has never been explicitly tested, to our knowledge, in Orchidaceae. Angraecoids (Vandeae: Angraecinae) present a diverse rangeof chromosome numbers which makes them a good study system to understand karyotype evolution and its role in cladogenesis. Within Angraecinae, two major clades are recognised: one mostly confined to Madagascar, where only x= 19 is reported; and the Afroneotropical clade, which apparently presents a rare example of ascending dysploidy in the orchid family, with c. 90% of its species inferred to have x = 25. In this study, we aimed to trace the evolution of the chromosome number in the Afroneotropical cladeand to test, for the first time, the likely impact of chromosome changes on diversification in Orchidaceae. By using a near-comprehensive phylogenetic tree of angraecoids at the genus level, including 280 species, we mapped the chromosome counts of 116 species in 35 genera. Accordingly, we inferred the ancestral haploid number of most Afroneotropical angraecoid genera, starting from x = 19, and we identified a total of three first step ascending dysploid events in Conchograecum(x= 21), Dendrophylax(x = 22) and in the ‘Aerangidinae’ (x= 25); and a single first-step descending dysploidy occurrence in Calyptrochilum(x = 17). Within the Aerangidinae clade nine independent second step descending dysploid events were identified, which define new generic and suprageneric synapomorphies, namely in Ancistrorhynchusand Microcoelia(x= 24); and in the Cyrtorchis-Tridactyleclade (x= 23). Furthermore, two secondary and one tertiary dysploid events were identified in Aerangisand Summerhayesia, respectively. Finally, nine neopolyploid events were identified in eight genera. These findings have allowed us to test whether there was a significant contribution of chromosome number evolution to the radiation of angraecoids in tropical Africa