His research focuses on patterns and processes of evolution in the Californian and Hawaiian floras, with a special interest in lineages that span continental and oceanic-island systems. Bruce’s principal efforts have been to re-examine general evolutionary and biogeographic hypotheses in light of new perspectives offered by molecular phylogenetic and experimental approaches. Much of his work has centered on the Californian tarweeds and Hawaiian silversword alliance, which provide diverse examples of how plants from a common lineage underwent evolutionary change in highly contrasting environments. Bruce received his Ph.D. from the University of California, Davis in 1989.