Ancient hybridization in Curcuma (Zingiberaceae)-Accelerator or brake in lineage diversifications?

Hybridization is a widespread phenomenon in the evolution of plants and exploring its role is crucial to understanding diversification processes of many taxonomic groups. Recently, more attention is focused on the role of ancient hybridization that has repeatedly been shown as triggers of evolutionary radiation, although in some cases, it can prevent further diversification. The causes, frequency, and consequences of ancient hybridization remain to be explored. Here, we present an account of several events of ancient hybridization in turmeric, the economically important plant genus Curcuma (Zingiberaceae), which harbors about 130 known species. We analyzed 1094 targeted low-copy genes and plastomes obtained by next-generation sequencing of 37 species of Curcuma, representing the known genetic diversity and spanning the geographical distribution of the genus. Using phylogenetic network analysis, we show that the entire genus Curcuma as well as its most speciose lineage arose via introgression from the genus Pyrgophyllum and one of the extinct lineages, respectively. We also document a single event of ancient hybridization, with C. vamana as a product, that represents an evolutionary dead end. We further discuss distinct circumstances of those hybridization events that deal mainly with (in)congruence in chromosome counts of the parental lineages.