Using phylogenetic approaches to test hypotheses on a large scale, in terms of both species sampling and associated species traits and occurrence data—and doing this with rigor despite all the attendant challenges—is critical for addressing many broad questions in evolution and ecology. However, application of such approaches to empirical systems is hampered by a lingering series of theoretical and practical bottlenecks. The community is still wrestling with the challenges of how to develop species- level, comprehensively sampled phylogenies and associated geographic and phenotypic resources that enable global- scale analyses. We illustrate diculties and opportunities using the rosids as a case study, arguing that assembly of biodiversity data that is scale- appropriate—and therefore comprehensive and global in scope—is required to test global- scale hypotheses. Synthesizing comprehensive biodiversity data sets in clades such as the rosids will be key to understanding the origin and present- day evolutionary and ecological dynamics of the angiosperms.