To mitigate the effects of the current biodiversity crisis – the rapid loss of species and ecosystems – we have to understand how species evolve and how diversity is assembled. Physical distance and ecological differences can influence gene flow among individuals of a species in different ways, including the emergence of new species. As such, the evolution of diversity is often driven by geographic isolation and environmental adaptation, but the relative contribution of these processes on species diversification is not well understood. TropAlp aims to study the dynamic interplay of these two processes in driving the evolution of plant diversity to gain a better understanding of the abiotic factors fueling diversification. I will focus on two biodiversity hot-spots, the tropical alpine environments of East Africa and South America, that show differences in diversity among lineages and regions. Both ecosystems are considered island-like with similar climatic conditions but are isolated from their tropical surroundings. The key difference between them is the extent of isolation between mountain peaks. This difference permits investigating the factors that cause variation in diversity using multiple plant lineages and will contribute to a generalized and more global understanding of the evolution of diversity. The objectives of this action are (1) to delimit species; (2) to elucidate the interplay of geography and environment on diversification, and (3) to compare differences in diversity and its causes across the two continents. TropAlp enables me to apply modern phylogenomics and population genomics with comparative analyses, model-based approaches, and bioinformatics. While I have expertise in the latter, comparative phylo- and population genomics are the expertise of the host laboratory. This action will provide me with a modern skill set to become an independent, critical thinking researcher and will enhance my career chances.