Evolutionary history of Chrysosplenium L. (Saxifragaceae): a molecular phylogenetic approach to dispersal and diversification processes

The diversification of plant lineages is often governed by intricate interactions among geography, climate, and lineage-specific traits. The genus Chrysosplenium (Saxifragaceae), a herbaceous group with a disjunct distribution across the Northern Hemisphere and parts of South America, serves as an excellent model for exploring the mechanisms underlying plant diversification and historical biogeography. In this study, we reconstructed a comprehensive phylogeny of Chrysosplenium by integrating plastid and nuclear DNA markers. We also estimated divergence times, inferred ancestral geographic regions and distributable climate classes, and quantified colonization rates among ancestral regions and distributable climate classes to better understand the processes shaping the genus’s present-day distribution and regional diversification hotspots. Our analyses suggest that Chrysosplenium originated in the Eocene within cold climate zones of East Asia, from which it subsequently dispersed into Europe, North America, and southern parts of Asia. The genus underwent episodic diversification likely driven by climatic fluctuations that promoted both range expansion and lineage divergence. Ancestral distributable climate classes reconstructions indicate that early species had already adapted to a spectrum of cold and temperate conditions. However, despite the existence of climatically suitable areas beyond their current ranges, most species remain geographically localized. This pattern implies that factors beyond macroclimatic suitability—such as physiological constraints like water-use efficiency and habitat specialization—may restrict range expansion and foster allopatric speciation. Overall, our findings highlight the value of combining phylogenetic, biogeographic, and ecological perspectives to uncover the evolutionary processes shaping plant diversity.