Climatic oscillations, dispersibility and adaptability behind worldwide mountain radiations of the Helichrysum– Anaphalis—Pseudognaphalium (HAP) clade (Compositae)

Abstract Background and Aims Mountain ecosystems are recognised as biodiversity hotspots. However, the origins of their remarkable diversity remain unresolved. We explore this question by focusing on the HAP clade (Helichrysum-Anaphalis-Pseudognaphalium), a megadiverse lineage within the Compositae family that spans tropical and temperate mountain and lowland systems worldwide. The existence of multiple high-elevation clades provides an opportunity to address hypotheses regarding the impact of trait innovation, climatic oscillations, dispersal and niche lability in the diversification of mountain lineages. Methods To investigate the biogeographic history and diversification dynamics of the HAP clade, we built a time-calibrated phylogeny of 560 taxa (62% of the species) based on 989 nuclear loci. We examined the frequency of inter-mountain dispersal and lowland-to-mountain transitions and vice versa, tested whether diversification rates were dependent on time, climate or species diversity, and assessed the impact of bract colour on diversification rates using state-dependent speciation-extinction models. Additionally, we reconstructed the evolutionary history of two functional traits (bract colour, life form) and ecological preferences (elevational range, habitat) and explored potential correlations between them. Key Results The HAP clade extensively speciated during the Pleistocene, when net diversification rates nearly quadrupled, coinciding with parallel mountain radiations on multiple continents. The clade followed a pattern of nested radiations, with southern African mountains serving as initial diversity source and other mountain systems acting primarily as sinks. High-elevation ecosystems also contributed to lowland biodiversity. Diversification rates in high-elevations are independent of bract colour, yet significant trait-environment associations were supported. Functional traits and ecological preferences evolved repeatedly, with a tendency toward montane open habitat ecologies and chamaephytic life forms. Conclusions Our findings suggest that mountains do not fit the classic island model for the HAP clade due to its high permeability across heterogeneous environments, high dispersibility and ability to thrive in both high- and low-elevations. However, the clade’s evolutionary lability enabled repeated trait acquisition, niche shifts and microhabitat specialisation. This, coupled with Pleistocene climatic instability, likely played a significant role in driving allopatric and ecological speciation at different geographical scales.