Unravelling a rapid radiation: biogeography and niche evolution of Carex sect. Echinochlaenae Kük. (Cyperaceae)

Abstract

Aim: Carex section Echinochlaenae has a disjunct distribution across the Southern Hemisphere. It displays a clear center ofdiversity in New Zealand coupled with extreme morphological and ecological diversification, suggesting a potential evolution-ary radiation. We aimed to reconstruct the biogeographic history of the group and evaluate bioclimatic niche evolution duringcolonization and diversification events.Location: Southern Hemisphere, with emphasis in New Zealand.Taxon: Carex section Echinochlaenae (subgen. Carex, Cyperaceae).Methods: An integrative approach combining phylogenetic-phylogenomic, biogeographic and bioclimatic data was used. Wereconstructed a Hyb-Seq phylogenomic backbone, as well as an expanded Sanger-based phylogeny (ITS, ETS, matK). We inves-tigated the biogeographic history of the group's Trans-oceanic dispersal across the Southern Hemisphere through ancestral areareconstruction. Bioclimatic niche evolution was explored at different spatio-temporal scales by modelling environmental spacefor close sectional lineages (Distantes, Africanae, Echinochlaenae) and for disjunct areas within Echinochlaenae.Results: Both Sanger-based and phylogenomic reconstructions retrieved a monophyletic sect. Echinochlaenae, but with lowinternal resolution, topological incongruences and conflicting genomic concordance factors (low gCF vs. moderate-high sCFvalues) affecting certain key nodes. The lineage dates back to the Early Late Miocene (c. 10.7 mya), while cladogenesis is con-centrated around the Miocene–Pliocene boundary. Abiotic niche space of the group in New Zealand was relatively similar bothbetween closely related sections and disjunct areas in sect. Echinochlaenae.Main Conclusions: The complex evolutionary relationships and their ecomorphological differentiation in New Zealand arecompatible with a rapid radiation process likely involving mechanisms that rapidly increase genetic diversity and are probablyresponsible for the lack of phylogenetic signal even though it is a relatively ancient radiation. New Zealand acted as the ancestralarea and hub of in situ diversification for this lineage, and as a source of recurrent dispersal events shaping its disjunct distribu-tion. Abiotic niche conservatism predominates across large evolutionary and geographic scales. Given the disjunction from itsclosest relatives, this suggests that niche amplitude is determined by internal constraints.