A tale of two lineages: comparative biogeography across the Southern Cone of two South American Carex (Cyperaceae) groups

Abstract

Background and Aims The Carex phalaroides group and Carex sect. Bracteosellae are two species complexes that exhibit similar distribution patterns, despite being two evolutionarily independent lineages. Their centre of diversity is displayed on the eastern coast of the Southern Cone, with disjunct lineages that have successfully colonized and diversified in central Chile and throughout the central and northern Andes. Given the scarce research about the biogeography of herbaceous lineages in the Southern Cone, our aim is to elucidate their evolutionary trajectories and compare their biogeographical histories from a macroecological perspective, considering the major geoclimatic events in these regions. • Methods We conducted Hyb-Seq phylogenomic analyses for both groups. We followed a bioclimatic approach to trace their historical biogeography across South America; thus, we estimated the divergence times, reconstructed their ancestral areas and characterized their ecological niches, inferring their climatic preferences over time. • Key Results The C. phalaroides group displayed a more evident vicariant pattern than sect. Bracteosellae on both sides of the Arid Diagonals during the earliest cladogenetic events. Both groups displayed synchronic diversification processes, specifically regarding movements between the Pampa–Atlantic region, colonization of the northern Andes and differentiation within the Yungas. Bioclimatic analyses retrieved a clear separation between eastern and western lineages within the C. phalaroides group, with C. via-montana exhibiting a distinct shift in temperature-related variables. In contrast, this geographical structuring of bioclimatic preferences was not observed in sect. Bracteosellae. • Conclusions We identified several geoclimatic events as key drivers of diversification. The Mid-Miocene Climatic Optimum and subsequent marine transgressions probably facilitated the expansion of the C. phalaroides group ancestor beyond Patagonia. Both South American Dry Diagonals acted as major barriers, fragmenting a once broader distribution and promoting speciation through vicariance. The Andes Cordillera functioned as a south-to-north biological corridor for both Andean lineages. Following vicariance and isolation, both groups evolved broad ecological niches, reflecting adaptive specialization to diverse environments.