If you had been in northern Canada 45 million years ago, you might have encountered the distant ancestor of all of the oaks in the Americas. That single species gave rise to 220 more and two distinct lineages—red oaks and white oaks—that moved south through the boreal zone to populate large swaths of the continent all the way into Mexico. These two findings—simultaneous evolutionary diversification in the red and white oaks each following the same geographic routes; and two relatively recent origins of the Mexican oaks—are a surprise conclusion to a scientific mystery that went unresolved until now. Research published this week in the journal New Phytologist tells this story of the evolutionary history of American oaks for the first time.