Mountain ecosystems worldwide are recognized as biodiversity hotspots, hosting high levels of plant diversity that contribute significantly to global angiosperm richness. Similar to oceanic islands, these systems often exhibit distinct boundaries, isolation, limited size, and restricted dispersal, making "sky islands" ideal for studying macroevolutionary and biogeographic processes. Here we investigate whether diversification rates are higher in mountain systems compared to lowlands and explore the drivers of diversification in high-elevation habitats using the HAP clade (Helichrysum-Anaphalis-Pseudognaphalium), a diverse subcosmopolitan lineage within the Compositae family. We built a time-calibrated phylogeny of 560 taxa (including 62% of the HAP clade) based on 989 nuclear loci to infer the most probable biogeographic history and assess diversification dynamics. Furthermore, we tested the role of five functional traits in diversification using state-dependent speciation and extinction models. Our results revealed that the net diversification rate nearly quadrupled around 1.2 Mya , coinciding with the Mid-Pleistocene Transition, a period marked by intensified glacial-interglacial cycles . This spur in diversification coincided with an increased species accumulation out of continental Africa, suggesting that adaptation to new ecological opportunities played a critical role in shifting diversification dynamics. Approximately 50% of dispersal events involved niche transitions from high-altitude to lower-altitude environments, predominantly during the late Pleistocene, starting a new trend within the lineage . Diversification in the mountains was independent of the tested functional traits, although simulations suggest potential associations. While the analyzed traits likely offer evolutionary advantages in montane habitats, the high intra-clade diversity and the variable effect of traits across geographically distinct mountain systems may obscure a clear trait-diversification association. In sum, our findings underscore the complex evolutionary history of montane lineages and the dynamic interplay between traits, ecological opportunities and macroevolutionary processes in shaping biodiversity.